What is the smallest iron golem spawner?

12 doors on a side with 4 villagers per side. The vilage 'center' is the middle point between the the 'doors' that are considered to be part of the village. The golems will spawn in the middle and fall thru. DocM has a nice tutorial on youtube describing the mechanics in detail. 20x20x8 footprint for the main cells.

It could be that your layouts dont lend themselves to having a natural 'middle' Even the 2nd picture with the doors all clustered together in the middle, there might not be room for the golem to spawn because the doors are there.