The room must have the following conditions:
1) 4X4 Amos – approx. 6 feet by 6 feet.
2) 2 door posts and a lintel.
3) Ceiling
4) According to some, a door (we put on even without a door)
5) A doorway above 10 Tefachim.
6) Be for living purposes
7) Not a room for purposes not honorable for the Mezuzah, or a shower room.
8) Permanent living.