stables (the plan was to brainstorm more about this when #387 is done, since you'll be able to sell pets)
original: Stables will not yet be implemented. I think it's fine to explore this later when pets are tradeable / sellable. Maybe pets in the stable could go "over max" on some stats, unlocking a hidden level of capability they didn't know they had. Instead of gold, this would take time (the building would not be upgradeable) -- probably, a week per pet per level. Pets will gain a new "overmax capability" stat (hidden, not upgradeable) that will determine how many levels they can go over their maximum. Additionally, not every stat will be able to go over max; some might have 2 levels over, some might have none.
barracks
original: upgrading this would allow you to attack a guild x times per day, within a certain level/member count range of you. Everyone in both guilds would be involved (provided they're online). This would not require consent of the other guild. Attacks would be calculated on a weekly basis, with upgrades following a similar (albeit, more expensive) path -- 1m, 2m, 3m -- etc.
raid simulator
original: I'm not sure if this should be "buy a boss" or "buy a building, and upgrade it to unlock different statistics to test a boss with" or what.