Hello!
I will be sharing below what I think and what in my opinion is, the best way to build the garrison while leveling up, and when one reaches the end game already.
TH 2
GOLD MINE
In this game, there are four very important resources which one will always lack. Gems, gold, job keys, and fodder. Gold mine is very important early game, until you get your equipment sets. Also, early on, the buildings are quick to build, so the Worker's Hut is useless.
TH 4
ARMORSMITH
Having the smithy up early and running allows you to forge 3* early in the game, giving you a better foothold in the story quest. Also, the Alchemy Lab is useless early in the game, it only becomes useful at the end (more on this later).
For 4* gear, you need 100 copper ores + 10 of 2 variants of 3* tier raw material.
For 5* gear, you need 200 copper ores + 10 of 2 variants of 4* tier raw material.
IF YOU WANT, YOU CAN CREATE THE ALCHEMY LAB, THEN DESTROY IT, JUST TO FINISH THE QUEST TO BUILD ONE.
TH 6
IRON QUARRY
You will need a lot of copper ore for the armorsmith, so you will want this building up and running as quick as possible.
IF YOU WANT, YOU CAN CREATE THE FARM, THEN DESTROY IT, JUST TO FINISH THE QUEST TO BUILD ONE.
TH 8
MARKETPLACE
There are a lot of debates on this one - Marketplace vs Salvage Yard. I personally prefer the marketplace however. First of all, the marketplace gives a lot of good items (although a bit expensive, but I personally got some 5* potentials from it.) Secondly, the items you get from the salvage yard can be gotten from the fusion altar + iron quarry + farming.
As requested, samples of items sold in the marketplace at max level (not all, others credited to whodahackii):
3-4* Hero Ticket - 100k gold
3* Hero Ticket - 50k gold
2-4* Hero TIcket - 20k gold
100k Gold - 15 gems
2 Job Keys - 10 gems
3 Arena Orbs - 10 gems
3* Stat Rune - 50k gold
15 Energy - 40k gold
2x 5* XP Potion - 30k gold
5x Express Tix - 25k gold
Random Potions - 8k-20k gold
3x Seeds/Ores (3-5*) - 25k gold
Weapon/Armor Tickets (3-5*) - 10k gold
50 Blood Tokens - 15 gems
4 Silver Hammers - 40k gold
3 Gold Hammers - 20 gems
5 Green Hammers = 20k gold
3-4 Stat Runes/Skill Runes = 15-25 gems
IF YOU WANT, YOU CAN CREATE THE SALVAGE YARD, THEN DESTROY IT, JUST TO FINISH THE QUEST TO BUILD ONE.
TH 10
WISHING WELL
The wishing well is one of the most important buildings in the game, at max level, it gives you 5 wishes that gives gems, gold, hero draws, job keys, etc. On the other hand, the Merc Camp is utterly useless with friends and strangers in the game.
IF YOU WANT, YOU CAN CREATE THE MERC CAMP, THEN DESTROY IT, JUST TO FINISH THE QUEST TO BUILD ONE.
TH 12
FUSION ALTAR
The fusion altar's expedition gives gold, and will also help you form those rare ingredients for the armorsmith. On the other hand, the weapon forge is useless in the early levels, when you get to level 20 however, it's a different story.
You can switch to Weapon Forge by TH18 (you can make 5* weapons by then), but make sure you create as much 4* mats for the armorsmith before then.
TH 14
WORKER'S HUT
At this point in the game, the buildings are starting to take ages to build. Furthermore, the worker's hut gives silver hammers at max during expeditions, which is a necessity when upgrading weapons. At this point in the game, while the towers sound nice, you don't need them. I would not suggest building the towers at this point to destroy them for the quests however, as you'll be building them eventually when ready, also, they are a bit expensive so doing so is a waste of resources.
TH 16
ACADEMY
Academy provides you job keys and promotion tokens, while Training Camp doesn't really give anything. Also, at this point in the game, you are probably on the way to creating more 5*s for use or limit break, so academy will help out a lot. Expeditions also give keys.
TH 18
WATERMILL
Energy is very important in the game, especially during events. On the other hand, while still growing up, the small stat additions from the towers aren't really helpful at this point in time. Getting better hero/gear/higher max levels is more helpful, and energy allows you to do just that.
*EDIT* - I suggest switching to Forge at TH18 (you can max it and make 5* weapons then), but before that, convert as much of the 4* mats as you can for the Armorsmith. When you get enough 5* weapons, or most of them, feel free to switch to Altar for the expedition and fusion again.
TH 20
GEM CAVERN
There is not much to say here. A building that generates the premium currency, why not?