My Lands: Black Gem Hunting

Hey, I'm thinking of getting a clan castle for my clan sometime in the near future. There are several castles that we could take down around us, but I'm just wondering about the building cost for inside the castle. I couldn't find anything about building towers or unit factories on the encyclopedia.

This is the "forum rules" category...

And I've really no idea what I'm doing. I'll try to post it one the appropriate wall, but I'm not sure how to do that.