Cheap no redstone iron farm

A starter iron farm for three villagers and one zombie, built from cheap materials with no redstone. The zombie sits in a boat where the villagers can see him and the golems drop into lava over the hoppers. The whole tutorial runs three minutes. Java only.

Build at least 50 to 120 blocks from the nearest village. The creator gives both figures in different replies, so take the larger one.
If the iron sits in the hopper instead of reaching the chest, the hoppers are not pointing into the chest.
Put the villagers in place before the zombie, and do not open the trapdoor too early.
One builder ran several of these about 20 blocks apart with no problem.