Building destroyer acts a bit weird right now, and is generally not very detailed. It also, really underpowers normal creatures, why can't a goblin take down a wooden door? So here's my suggestion.
[BUILDINGDESTROYER: 1]- All large creatures, such as goblins, dwarves, elves, etc. (without higher tags) would have this. Could destroy all wooden objects, windows, cabinets, tables, chairs, statues, that sort of thing.
[BUILDINGDESTROYER: 2]- Larger creatures (lions, tigers, bears, animal-men, etc.) would have this. Destroy all above objects and hatch covers, workshops, etc.
[BUILDINGDESTROYER: 3]- Large/strong creatures such as elephants, whales, etc. would have this. Could destroy all above and unlocked doors, levers, drawbridges, open floodgates, etc.
[BUILDINGDESTROYER: 4]- Getting into semi-megabeast territory. Large and strong creatures like giants, trolls, ettins. All above objects, locked stone doors, closed stone floodgates, etc.
[BUILDINGDESTROYER: 5]- Weaker megabeasts, demons. Could destroy all above, pumps, traps, constructed stone things (walls, floors), etc.
[BUILDINGDESTROYER: 6]- Strong megabeasts, demons and
Could destroy all above, metal
uilt objects (doors, floodgates, hatches, etc.), traps and small stretches of natural tiles (dirt, stone).
Nothing can destroy metal constructions, smoothed tiles or ore.
Building destroyer would also be tied to reasoning or whatever. A berserk dwarf or goblin would destroy stuff indiscriminately, where something smarter would only destroy stuff in it's way, and something REALLY cunning would destroy the floodgate holding back magma or something like that.