You're sitting in the graveyard, your new upgraded level 2 garrison has grown, and now you don't know what to do or what to put. So many options and you don't want to make a mistake. Thankfully, we've done to the research for you so that you know which buildings to put down. The following buildings are the best buildings, so building them will mean you'll do great no matter what. Later in the game, with more experience, you may want to switch some out, but for now and especially for those starting, this is the list for you.
#1 Building - Profession Buildings
These buildings are going to be what you want when you want it at all times. In the beta, there was a lot of debate over if you super duper had to have the profession building for your profession, but now during the live game it's kinda obvious you're going to want the buildings for your specific profession just because to craft anything you'll need BoP resources that only those buildings can create. So if you have two professions, with three alternate profession buildings, you're gonna have a bad time. Hexweave Cloth is soulbound and required for most everything, so good luck crafting without a profession building.
Of course, you can have two personal professions and any number of other buildings (up to three really), but how far are you going to go without crafting mats? You can make old world stuff, which the dreanor NPCs can't make, which is nice, but what's that worth? You can make something like one a day or so with just your profession for a lot of materials as well. A level 5
#2 Building - Dwarven Bunker / War Mill
WAR IS UPON US and this is where all your war is going to be happening at. It first of all gives you Apex crystals for Garrison Resources which are used to buy raid gear (WOOHOO), it gives you a free Seal of Tempered Fate which this luckydoo gives you an extra roll chance in the raid finder in WoD. Come on, what isn't to love? Seriously, let me ask that, what isn't to love about something that just hands out everything you could ever want in the game.
#3 Building - Barracks
The Barracks is almost a requirement until you get enough followers that you don't need it anymore. Patrol missions grant extra follower XP and are super useful for getting your followers up to level 100. In addition, it gives you the ability to have a bodyguard in Dreanor (sweet) assuming it's level 2 and you have a follower with the Bodyguard trait. The level 3 isn't as worthwhile to some, it grants you 25 followers instead of 20. This requires the dedication to spend the resources for it, but... it's very useful to run more missions.
Considering the large alternatives (Mage Tower teleports go to ... weird places you probably will not want to be at level 100, the stables is for mount collectors, and the goblin/gnome workshop has severe limitations to the use of the items it creates), the bunker/mill and the barracks are the way to go at least at the start and even then some.
#4 Building - Lumber Mill / Trading Post
High five for these two awesome buildings, they give you additional Garrison Resources which you'll run out of quickly. They both operate on the same wavelength, the Lumber Mill gives you work orders for trees you "harvest" (more like collect) out in the world while the Trading Post lets you trade crafting materials, gain more resources, and also gives you the ability to have an auctioneer and opens up another faction (woohoo).
#5 Building - Frostwall Tavern (early game) and Gladiator's Sanctum (end game)
The tavern at level 2 is insanely good as it lets you flesh out your followers by recruiting ones with specific skills, meanwhile the sanctum at higher levels just give you great PvP bonuses and makes your life a better place throughout Dreanor.
Have fun and see you all in Azeroth!