Minecraft wiki entry for Building_a_metropolis, associated text: You can add mechanical floors at intervals which includes something like a control room that controls the redstone signal in the building.
Slaughterhouse Build a medium-sized building where unwanted animals are lined up to drown or burn (not with lava though) or whatever suits you. Collect their drops and give them to meat and/or wool shops. Note: Do not build this if your city is a Peaceful Place.