I have built my garrison up with leveling and questing in mind. I have no doubt that once I upgrade to garrison level 3 or if I choose to raid in this expansion pack, my build will change.
Dwarven Bunker (Large): The Dwarven Bunker has an awesome, if not the best Level 1 perk for leveling: It doubles your chance of receiving a random item upgrade from quest rewards and increases the potency of the upgrade. So instead of receiving a green or blue quest item, I quite often receive blue or even purple items instead. It works on any quest reward, including followers by the way.
Lumber Mill (Medium): It is to my understanding that until you are at least at garrison level 3, the Lumber Mill is probably your best best since it yields extra garrison resources for poking at trees that you find while out and about in Draenor. It takes a little under 13k garrison resources to upgrade to level and I think someone calculated it out to be a month’s time approximately, so every little bit helps.
Enchanter’s Study (Small): The enchanting building is great if you don’t have enchanting or anyone to hitch a ride off of since it lets you disenchant gear in your garrison. If you do have enchanting, it allows you to get patterns and extra mats. Between my two professions, I find enchanting more useful than blacksmithing.
Salvage Yard (Small): Allows you to receive Salvage from missions, which have a chance of dropping items for your followers or something like that. I’m taking the Internet’s word on this one. I just built this and have not receiving anything useful to date.