Ah I see, so its randomized slightly so someone could have all rooms slightly smaller if they're really unlucky?
No, all rooms are the same size for all players, its just the order the rooms are unlocked are in a predetermined order.
1. House built
2. Room size increase
3. Back room
4. Left room
5. Right room
6. Upstairs room
7. Basement room
3-7 cannot have their size increased.