A house is defined by a door or a bed with a roof over it. There can only be one house 
in a 3*4*3 box. You need at least 16 houses in your guild to have chance of spawning a villager.
The chance of spawning a villager is:
 points/(Area of the guild/64)
 
The maximal amount of villagers possible in one guild is:
 guild area / 64

The villagers spawns at the .guild return point. There has to be at least a lightlevel of 8.
