Set a trigger, that when you move close enough to the dood, a scripted sequence triggers that makes him walk over to the place with the roof. You set the target on the scripted_sequence to maybe a func_train, with some avelocity, to ,go tumbling down on the dood, and be sure to turn the damage up REAL HIGH so he dies.... and maybe a custom sound that has the same targetname as the train that sounds like a roof breaking... That would work..