just some thing i was thinking of...

[Hypolite]

This would not work for a number of reason:
- Only rock roof collapses into character-murdering rock, you would deal at most 65 damage with thin roof collapse
- In the case of building, roof collapses until there is 7 square to the nearest pillar, BUT
- If you removes outer walls, the building roof disappears and can't collapse
- You can actually make a large portion of rock roof collapse, but you have to completely mine a rock formation, put a pillar and you only need to sell it to make the roof collapse, BUT
- Since you want some sort of choke point, you would have to build walls to direct raiders, which would support the roof, cancelling the idea.

[Keyreper]

I believe we have a new atom smasher!

sounds interesting!