Simple Three villager starter iron farm

A single module iron farm with three villagers, three barrels and one zombie sitting in a boat. The villagers panic at the zombie, golems spawn in a small pit beside them, and water pushes them onto lava with one hopper and chest underneath. It is small and cheap, and several builders repeat the module around one shared kill chamber to scale it up.

• Golems spawning everywhere except the pit is the most common failure. Convert the grass and dirt around the farm to path blocks with a shovel, roughly 6 to 15 blocks out, add slabs on any remaining spawn spots, and fill in holes and caves underneath.
• Do the pathing before you put the zombie in. Several people had to tear the farm down and redo it.
• The barrels are not optional. Without a workstation the villagers stay up on the beds, cannot see the zombie, and the farm only produces at night.
• The villagers must have slept, and they need to have slept within the last 20 minutes for golems to spawn. Lying in the bed once is enough to count.
• The zombie burns in daylight. Keep slabs above the boat, and add more if it still dies. The wooden slabs on the border can catch fire from the lava, so stone slabs are suggested instead.
• If the boat sits too close to the bed the zombie can convert a villager. Back the boat up slightly, keeping it under the slabs. When building more than one module, keep the villagers at least 16 blocks from the other module's kill chamber or they detect that golem and stop spawning.