My friends and I have been playing with these building rules for a while now. The need arose when we tried to make custom rules for buildings in Apocalypse scenarios and ended up with a game with nigh-impervious buildings that made a few units ultra-powerful, and where we ended up having to make up rulings on the fly because the rules we'd come up with just had to cover too many possibilities.

So these building rules are a replacement of the rules in the BRB. They offer a skeleton to build custom rules on to, but with more meat on its bones so that you don't have to invent the wheel over and over again. It also helps to keep your games from becoming unbalanced by adding buildings (even in smaller games), since they offer great defense, but now carry significant risk to the occupants (and sometimes those nearby!).