On the island during season one, there were three types of dwellings:

Shacks - Constructable after 1 drive kill, don't have keys, so anyone can come in. Sleeps one.

Cottages - Constructable after 10 drive kills, have 5 keys, and sleeps two.

Mansions - Constructable after 20 drive kills, have 15 keys, and sleep four to five. 1)2)3)

Additional keys can be cut, but they cost donor points. One can build 3 dwellings. And only one in a city, but you can purchase a second in a city, if you don't already own three dwellings.

Also see Housing. For a guide to Season Two dwellings, see Dwellings for Dummies.

1)
Not entirely sure which
2)
They sleep 5. My entire family sleeps in there. *grin*
3)
All occupancy numbers are doubled for Kittymorphs, since they just pile on top of each other.