Stackable module iron farm

Iron farm with four villager modules around one central drop. Each module holds three villagers with beds and composters and a named zombie on a piston clock: the zombie rises into view so the villagers panic and summon golems, then drops away so they can sleep. Golems spawn on the platforms, water carries them to the middle and they fall into lava, with hoppers feeding chests below. Iron and poppies come out. It suits a survival world with villagers and a few name tags ready, though the video is filmed in creative with flight, so plan scaffolding. Build it far from villages and villager breeders, or modules stay empty.

• No golems at first, or after the chunks unloaded: the villagers have to sleep in their beds once. Wait for night or switch the piston clock off for a night. Several builders report it.
• Golems snag on the walls, fence gates and top trapdoors on the way down. Add a fourth fence gate (a comment with 64 likes), or open the gates or leave out the top trapdoors.
• If a module stays empty, keep villages and breeders about 100 blocks away and check that its villagers see the zombie. An open trapdoor on the composter blocked it for two builders.
• Golems spawning on the ground below: make the ground under the farm path blocks or slabs, or build it over the ocean. Several builders report it.
• Keep the walls as walls. Glass in their place lets golems spawn inside it and suffocate. A comment with 66 likes says so.
• For a second layer, build it again about 30 blocks higher without lava and hoppers and drop its golems down the same shaft. Top comment on the video.