This is a huge schematic that includes eight (8) cobblestone generators and more pistons than I care to count. It will build a square room (roof and floor) and repair itself when the cobblestone is destroyed. It can be turned on and off from inside and outside so you will never get locked out or in!
PLEASE NOTE IF IT DOESN'T WORK IT IS BECAUSE YOU DID NOT "COPY AIR." FOLLOW THE RED-STONE WIRE COMING FROM THE MIDDLE AND MAKE SURE IT CONNECTS TO THE OUTSIDE CIRCUIT.