I know I'm basically rewording your idea with mechanical switches. But does he even really need the diodes or the h-bridge, or any thing but electric switches at all for that matter? It seems like a four pole switch (2 NC 2 NO, I have a few of these so they cant be uncommon) for user control could be set up with both leads closed one way in one position and both leads closed in the opposite direction in the other position, at that point you have a door that will move up or down continouously depending on the switch position. Then set up an NC switch the top to kill the power to the circuit that makes it move up when it hits the top, and another to kill the downward circuit when it hits the bottom. (again, sorry for basically just rewording your idea with a little variation, but the guy is a beginner)