or...
make a func_breakable for the ceiling... call it "myceiling" for now... set it to target "ohmygoditsfalling"
then make a bunch of other func_breakables below it... texture them with whatever... set rendermode to texture... then fxamount to 0... this will make them invisible... set material type to rocks... and name them all "ohmygoditsfalling".... now... when the ceiling breaks... it triggers all those other ones... and you have a big mess of sprite based rocks falling everywhere
yay... ps... to inflict damage... you need to set a trigger_hurt where the player will be standing... and target it through a trigger_relay named "ohmygoditsfalling" with a delay long enough to let the rock sprites reach the player...
-Chippy