Unless you have nothing better to do with Fps and Land.
There's
always something better to do with FP and land than build the Colosseum, Notre Lame, and/or Waste of Space Needle.
Well, here's my view on the GBs in the game. Some of it's opinion, and some of it are just impressions of the higher age BPs in the game, since I have no experience with them. But I've looked into most of the GBs when planning my city, and looked at the strengths and weakness of them to see which were worth having and which weren't.
There are some GBs that are simply never worth it no matter how you play. Colosseum tops the list for three reasons: it's happiness is rubbish even for IA, and it only gets worse, the medals it produces are too small to be worth building, and it's got a gigantic footprint for it's age. Notre Dame has just happiness and flat supply production, both of which will eventually become obsolete as you level. The Space Needle is similar, except that it produces coins rather than supplies, but it's still crap and it's a space hog.
Otherwise, how are you playing the game? Are you a fighter, and if so are you just fighting PvP for the towers, are you an active plunderer, or do you fight in GvG? Are you a farmer producing large amounts of goods for your guild? Are you a merchant, acquiring goods by various means, and then selling them to players in exchange for fps on your GBs? Do you like forging into the unknown every week during the Guild Expedition? Play style makes a lot of difference when choosing your GBs. Also, I don't think it's worth the effort to build a GB that you'll just tear down at some point either, so you should know what kind of play style you have and choose the GBs accordingly. Don't just slap a GB down because you got all the blueprints and acquired the goods.
Generally speaking, a GB that has coin production, supply production, happiness or population as one bonus needs a very good bonus in the other spot to be worth building. GBs that have two of the above as both bonuses tend to be among the worst, with the exception of the Habitat. Largely it's because those bonuses don't scale as the player levels up, and the bonuses get too weak to be useful. However, some of the best GBs have one of those bonuses with a very good bonus. Another problem comes with population: it replaces the population production of your houses, but houses are also used to provide coins. So a population bonus can make you poor on its own, while your city can end up unhappy if you build too many houses to compensate. This isn't a problem if your city has a lot of low population buildings that produce coins, like the SoK, but those buildings are usually won through events. Medal bonuses tend to be kind of poor too, they produce small amounts of medals and appear on mediocre GBs at best.
The good bonuses that appear on multiple GBs are generally the attack boosts, fp production, and goods production. Some of the unique bonuses are very good, while others are less useful.
Observatory is the "I'm a good team player" GB. It doesn't directly benefit you, but rather your guild. It was originally designed for GvG, and GvG guilds usually insist their members get one, but the goods production is useful for GE based guilds too. It's also one of the smallest GBs, and thus easy to work into a city design, it's also very cheap in terms of goods. The bps can be moderately hard to get. If you're not in a guild, or your guild doesn't play GvG or GE, then you can skip it.
Temple of Relics is unnecessary if you don't play GE, espcially since it has a fairly large footprint. But if you're going to play GE regularly, build it. You'll get better rewards, and the GE hands out ToR blueprints like there's no tomorrow.
Tower of Babel isn't bad. If you build it, it'll be for the goods, since the population isn't very high, and population disadvantages from this GB are negligible. There are enough goods GBs that you can do without it, particularly if you're a fighter. If you prefer to play as a farmer or merchant, then it should be in your city. Another upside is that it ties LoA for third smallest GB in the game.
The combat GBs, Zeus, Cathedral of Aachen, and the Castel del Monte are essential for fighters. If you fight, get them. If you don't fight at all you can live without them. The CdM may still be useful for FP production, and the Zeus is the smallest of all the GBs, so both can still help a pacifist city get through the continent map. CoA just has coin production as the other bonus, so it's the least useful of the three.
The Hagia Sophia like Algona said, is probably the most controversial GB in the game. It's not a bad GB, but its happiness is small in the later ages, and it has a fairly big footprint for an early age GB. However, fp production is one of the best abilities you can find on a GB. I would say that the Hagia is not a GB that you can jut put in your city and leave no higher than level 3 or 4. If you put it in, you're going to need to level it up to make it useful, and some people would argue it's not worth the effort. Make sure you plan you city around having this, and don't just slap it in because you got all the bps, and build it earlier rather than later.
Saint Basil's Cathedral is okay. The defense bonus is more useful if you're in a GvG oriented guild, since it boosts the guild's support pool, and some guilds may require it. But the defense bonus is less useful to the player. It's not worthless, but it's not essential either.
Deal Castle is pretty much a GvG GB. Like the Basil it boosts the guild's support pool with the defense bonus. The medal bonus isn't worth it. It's also one of the biggest GBs, which is another disadvantage.
Frauenkirche of Dresden is great for farmer and merchant types because of the goods production, and it's a decent happiness GB. But even fighters might find it useful. Don't rush to get it, but it's worth having.
The Capitol is mediocre at best, though some people seem to rely on it. It's got population and supply production, and like I said above these are bonuses that don't work well together. The main disadvantage is the population bonus. This
might be okay if you've got enough happiness from other GBs to compensate, and if your coin income is primarily from something like SoKs. I think it's among the worst though, and would not recommend it to a new player.
Alcatraz is one of the most popular GBs in the game, and it's pretty much essential for a fighter. The unit production is a very powerful ability, and the happiness bonus is good too. But if you don't like fighting, then this isn't a good GB to build. It's the biggest GB in the game, you won't need the units, and there are better ways of getting happiness.
The Atomium is another GB that is GvG oriented, since it provides guild goods production. The happiness bonus is also useful for a city. However, given that AF and OF goods have no use in GvG, that makes this building less useful than it was in the past, especially since it also has a very big footprint. I'll be honest though, I don't like the Atomium, I think it's ugly and it's a space hog, so that tends to worsen my opinion of it.
The Habitat is an interesting GB. Like I said above, population and coins are bonuses that are weak when combined with other weak bonuses, and population has the "poor and unhappy" problem, but it's not a bad combination here. That's because it's essentially a big house. It can be useful to replace a city's normal housing, thus freeing up space to build. More importantly, it doesn't require 2x2 roads like many houses from later ages do, which also gives the player more space. Not everyone likes this building or builds it, but it can be a useful part of the city's design. A possible downside is that it might be difficult to meet a city's population needs in later ages with this building alone (hard to say, because city design gets more complex later in the game especially with GBs and special buildings that can replace the functions of normal buildings).
Lotus Temple is similar to the Space Needle, since it has the same two poor bonuses. Possibly, as a GB that produces coins and happiness, it's meant to balance out the Innovation Tower from the same age. But it's not a popular GB at all, and few people build it usually because people who rely on the Inno are getting their happiness from a Traz and Atom, and their coins through SoKs, and don't need the Lotus.
I don't have any experience with the Dynamic Tower, though I'm trying to acquire one anyway. It looks useful, at least on the surface. It gives goods when aiding a building corresponding to the aided building's age. The advantage here is that the player can choose which goods the DT is producing by aiding specific buildings. One possible downside is that might produce goods in quantities that are too small to be useful. The other bonus is flat supply production, which is weak on its own. The opinions on this building are mixed, so I can't really say how good or bad it is without personal experience.
The Voyager V1 looked quite useful to me as an active PvP player, but when I looked for people to acquire bps, I had only 1 out of nearly 80 people on my friend list who actually had one. Then when I looked through the global rankings on my main server, the highest V1 I found was level 7. There's bigger Cols and NDs than that on the server! That just shows how popular this GB isn't. Maybe if you're an active plunderer, you might get some use out of it, but the plunder bonus only kicks in 3 times a day, which isn't much. That leaves you with flat supply production, which is not a great bonus. This one is only for the most harcore plunderers, just about everone else can skip it.
Rain Forest Project is a luxury GB. The increased chance of getting BPs from aid is pretty small, but it can be useful for getting those BPs to unlock levels past 10. Goods production is a useful ability, but there are several other GBs that make goods. So it's not useless, but you could live without it.
Gaea Statue is pretty much a scaled up Col, and that's known to be the worst GB in the game. The Gaea is much better than the Col, but that's because it's mediocre rather than utter crap. Still, it might be an okay choice for happiness for a pacifist city, because the medal production isn't too bad and pacifist cities won't be getting medals from a lot of fighting. Its 6x4 footprint is relatively small, unlike the bloated Col. It'll probably get worse as newer ages are introduced into the game though, and is likely a poor choice to invest in building, particularly since there are 3 rather than 2 AF GBs, and the other two are decent.
Arctic Orangery is another must-have for fighters. The critical hit chance is quite powerful, and it's paired with FP production, which is always good. A player should build all three combat GBs first and level them up before putting in this GB to get the most out of it. Main disadvantage is the large 7x7 footprint which makes it one of the biggest GBs in the game.
Seed Vault is still pretty new, but I'd classify it as a luxury GB. It has a small chance to give you a random item when you aid a player. These items are the same as produced by a Wishing Well, and supposedly have the same chances of being produced as a WW. One of these items are diamonds, which gives this building a lot of potential. To get the most out of the GB, you'll need a well-developed social network in the game. The other bonus is just flat supply production.
Atlantis Museum is the newest GB, and I haven't seen too many people with this yet. It has a chance to double plunder, and combined with some of the set buildings released this year, it's got a lot of potential to be great for a plunderer. Definitely much better than the V1. If the bonus kicks in, that's 10 fps from a properly set up Indian Palace set or Terrace Farm, and a significant chunk of loot from Zen Zones, Queen Statues, and so on. The other bonus is just standard goods production, which isn't shabby either. If you aren't a plunderer, then don't bother with it, since there are plenty of other goods GBs to fall back on. However, since two of my main sources of goods are GBs and plundering, this GB is definitely of interest to me.
Then there's the GBs that are good for any city:
Lighthouse of Alexandria/St. Mark's Basilica/Royal Albert Hall have production boosts, the SMB boosts coins, while the other two boost supplies. They all have a standard goods production bonues as well. LoA is usually considered one of the top 10 if not top 5 GBs in the game, it's small, it's easy to get, and it's always useful. This should be one of the first GBs any city should try to get. SMB is bigger, and boosts coins rather than supplies. RAH is a scaled up LoA more or less, but it's also one of the biggest GBs. You can hold off on that until later.
Chateau Frontenac has a powerful ability that increases coins, supplies, goods, medals, and diamonds from quests. This is best used when playing recurring quests over and over for the rewards, and there's a whole strategy devoted to it:
https://forum.us.forgeofempires.com/index.php?threads/cosmic-ravens-version-of-heavy-questing.15777/ Even at level 1, the Chat can increase the diamonds won from a quest by 50%, which by itself is a good argument for putting up this GB.
Cape Canaveral does only one thing: produce FPs. But like I said above, that's one of the best abilities in a GB, and it's moderately small for a GB, so it should find its way into any city eventually.
Innovation Tower is another very good building. It's got FP production, again good bonus. Biggest downside is its other ability which provides population. Like I said above, population reduces coin income, while requiring happiness. Still, you'll see this in most powerful cities, and it's providing the population needs rather than any normal houses, while SoKs are making the coins and a Traz is providing happiness, often with a FoD and/or Atom.
Last is the single best GB in the game, The Arc. Sure, it's cranking out guild goods, but that's not why everyone is building it. Everyone's building it for that other bonus. What does it do? It increases the prizes you win from investing FPs in everyone else's GBs: more FP packages, more medals (and this pretty much makes medal production GBs useless), and more BPs. That's why you see everyone jacking it up to level
80.
If you're an inexperienced player, and you're still trying to figure out what part of this game you like best, then I'd recommend going for the Zeus and LoA first and try to avoid going into a new age before you get them. ToB isn't bad to pick up early either. If you're playing the GE regularly and enjoy it, go for the ToR as well. If you're in a halfway decent guild, they may encourage you to get the Observatory, and possibly help you get it. Then go for the CdM and SMB.