Ceiling stuff

I'm not at my normal comp now, but I've been thinking of this cool thing to do when I get back to it. I don't recall ever seeing it in another wad before (although certainly there is one). In one level I'm making, you press a switch right next to the door to open it (SR Open (turbo)) and then proceed to get the blue key. You come back later (haven't worked all that out yet though) and the door is closed, but another one is open with mancubi behind them, which you have to kill to reach the door-open switch. What I'm thinking of doing is this: close both doors originally, but have one small sector behind each of the two doors. The one behind the mancubi door will originally have 0 for a ceiling height, while the one behind the other door will have 128. When you take the blue key, surrounding triggers will raise the sector behind the mancubi door (W1 up to highest ceiling) and lower the one behind the normal door (W1 down to floor + 8). Since doors only open to the lowest ceiling, the first time you hit the switch, the normal door will open. Later, you reveal the mancubi instead, and something behind them will raise that ceiling again so you can open the door.

Somebody already did this, I assume. Where can I see an example?

If you already know how to do it, then why don't you try it?

Well I'm not at my normal comp...