This is the link to the Repository in the Dungeon. There are a bunch of sticky threads that have lots of information. I don't know what your problem is specifically with adding a building but these should give you a starting point. Dungeon Repository
If this doesn't help and you haven't been promoted yet (the mods get busy and it takes a couple of days sometimes), just post a thread here and ask the mods to move it to the Dungeon.
Just out of curiosity, what are you trying to do with the mod? I haven't done any buildings, only units. But anyway, best of luck.