Smalls
1. Profession building.
2. Salvage yard. (not that important) Alt: Profession building 2 if you have 2 of them.
3. Storehouse. (not that important)
Medium:
1. Barn (for epic crafting materials)
2. Lumber Mill (to get garrison supplies faster)
Large:
1. Dwarven Bunker (Save a small amount of effort and get a bonus token for free)
2. Whatever.
Realistically, there is no 'ideal set up' as a raider as every single bonus provided by the Garrison is effectively quality of life (except for profession buildings, make sure you have your professions covered). Ideally you want a Dwarven Bunker to save a little effort, but even that isn't required. Pick the buildings with benefits you like, none of them matter all that much.