Stackable module iron farm

An iron farm with four modules built around one central drop. Each module holds three villagers with composters and a zombie on a redstone clock that keeps the villagers panicking. Golems spawn on the platforms, water carries them down the channels into lava, and hoppers feed two chests at the bottom. The modules can be repeated higher up to stack it.

• Walls are required. One builder swapped them for glass and the golems spawned inside it and suffocated.
• Golems hang up on the way down. The reported fixes are four fence gates instead of three, extra fence gates at the ends of the walls, and signs on both sides of every channel so the current picks them up again.
• The villagers have to sleep before anything spawns. Several report no golems at night, and one found it only started working once the villagers had slept.
• The trapdoors on the top platforms catch golems. Two builders put stairs there instead, or leave the trapdoors off.
• If only some of the four modules produce, extend the spawning areas by one block and raise the walls by two so golems cannot land on top of them.
• Bring more building blocks than the list says. The smooth stone count is short by about a stack.