Button::Make a small brush and with that button selected...press e and make the brush a func_button.
Now put a value in the entity properties window "health"-"1". That means it needs to be shot to work.Now lets work on trapdoor.
Well ur idea is not good as someone may shoot the button from far away... and the trapdoor gets a waste for high r_speeds. so according to me don't put health value. It is on ur choice as u r mapper.Add "target"-"trap1"
TrapDoor:Well now make another brush which you have to use as func_train and then in entity make the brush a func_train.
now add these properties:
"speed"-"400" (because it is a trap so it must be fast)
"dmg"-"0" (because the person may die before falling if 1 or 2 is set)
"targetname"-"trap1"
Now add 2 path corners where the train would move and come back to where it was. Hence,
DOne..... xA