AI is mostly for what units the computer builds, i thought the computer makes all buildings anywo. so if u want the computer to build custom buildings, u delete the standard ones in the AI editor and then put the custom buildings there
well.. i suck bad ass with the AI editor I watched and i saw u could only replace units, and not buildings. I think the workers will make the buildings theirselves if u just make it able to build for them (u can do that in the object editor)