What specific criteria are required to create a house for a villager in Minecraft?
The wiki isn't very clear on what constitutes a house. Simply, it says that a villager would consider a bed a house.
Does this mean that as long as there's an unobstructed bed, it won't matter what the building looks like?
Yup! Many villager farms are simple because large houses are not needed. Nearby beds should work (Though only one villager can use one bed. Multiple villagers can not use the same one bed.)