Building your Garrison up right is important. It's critical to understand that while you're leveling, you're going to have to be very careful in what you build and how you build it, because Garrison resources come fast and then end slow. When you reach level 100, outside of taking the effort to mine trees or trade resources, you'll get very few resources compared to when you're leveling. 

The first thing I suggest doing is keeping the barracks only as long as you need it and not upgrading it, unless you're a weaker class / have trouble out in the world doing PvE. The barracks gives you some awesome missions to help level your followers, but when you hit level 100 you'll find that most of your followers (if you use your garrison a lot) are at or close to level 100 and you can even boost your lower level characters with the level 100 missions from your followers. 

So this is how I suggest you plan things out. Get rid of the barracks as soon as you want to and get the war building, whatever one for your side, that gives you 50% chance of an upgrade with a quest item.  You're going to want this building because it also gives you a lot of other bonuses that are important, like the ability to get one of your seals (for raid rerolls) each week for free - one of the quests that you would have to do otherwise could cost you 1,000 Apexis Crystals! 

So let's get started. The first thing you're going to want to do is actually level your followers ASAP. Because at the start you're going to barely have enough resources to do much of anything, other than put up one or two buildings and maybe upgrade something around level 95. So, here is what you're going to want to originally place at barracks. 

Understanding Resource Spend 

As you level, any mistake in your garrison is going to be a major setback. Do not prescribe yourself to predetermined ideas, like needing crafting buildings, or needing everything to be placed in your garrison. If nothing else, go into it with a plan. What do you personally want out of your garrison? How do you want it to function? 

Upgrades are the WORST IDEA early on, except for a level 2 of crafting profession buildings. They are costly and will set you back from reaching the third garrison level unless you are very diligent about logging on and doing your missions to gain resources.  

You HAVE to put either a Lumber Mill or a Trading Post as your medium building. There is literally no reason not to, even if you want a stables or whatever. They will easily pay for themselves quickly, even if you keep them at level one, and it gets you more resources which you need. They are cheap to replace after your garrison is level 3 and farming trees or trading herbs has outgrown its usefulness.

Level 1 Garrison Build 

You're going to want the follow: 

• Barracks 
• Primary Wearable Profession Building OR Storehouse 

If you PERSONALLY PLAN ON CRAFTING your OWN GEAR SET, then put down your WEARABLE PROFESSION BUILDING. OTHERWISE, put down a storehouse. You get the profession building for freeish, well the blueprints from a quest which is great, however, if you're not going to craft gear for others or yourself (which requires a decent amount of farming and dedication), then don't even bother from this point forward. 

A storehouse is great, just because it gives you a bank. So if you're not crafting, don't feel pressured to give in and put crafting buildings in - some level 2 buildings have some great cool things like transmog weapon enchants for enchanting (and disenchanting no matter your enchanting level). 

Level 2 Garrison Build 

• War Mill / Dwarven War Bunker 
• Previously placed small plot: either primary profession building or storehouse. 
• Secondary profession building OR salvage yard OR just leave it blank. 
• Lumber Mill OR Trading Post 

Okay, so you kind of need to get to level 2 early on to get the medium plot up, which is going to be necessary early on to give you resources. This is the simple logic of it - the medium plot is going to grind you garrison resources, even if it's like 120 or so a day, for the next week or so. That's going to be almost 1k extra resources for literally sitting around and doing a bit of extra work while questing.  

The War Mill / Dwarven War Bunker is going to make you unstoppable in PvE because you're going to roll around in rares and epics while questing and at this point, you are going to be drowning in missions, so the barracks isn't going to compliment much. I went barracks, because I wanted the bodyguard, which helped me, but honestly get the War Mill up. 

Now, you have a resource grinding building up, which means you're going to be ahead of the curve in resources - more than enough to do missions, and you can start saving for not only level 3 but also your final build. 

With a storehouse, salvage yard, war mill, lvl 2 trading post, lvl 2 mine, you'll only need 850 resources which should be a joke to acquire while leveling. 

Level 3 Garrison Build 

Here is where you get to pick. You get one extra small (which if you're not a crafter, you can simply just place the crafting building you want to have fun with), one extra medium (which should be whatever you want at this point), and finally one extra large (a choice between stables and barracks). At this point, since you've reached level 3, you can do whatever you want.