I made a pair of dual fold doors for my workshop (so 4 leaves, about 2'6" each, making up a 10' door). Take up far less space when folded than normal folding doors meaning I can close them behind a vehicle which just fits in there. Just simple steel box frames with weld -on hinges and galv sheet riveted over them. Secured shut with a bar that swings across them from one side and drops into hooks on the back of each door. Obviously can't be opened from the outside though and I have another pedestrian entrance.