Cross the odd one out.

Answer:
1. cellar
2. maisonette
3. council flat
4. bed-sit
5. thatched
6. antique
Explanation:
In the above, we discover that they are the odd ones. Although there seems to be something that makes them similar but yet, they different in a way.
Cellar is the odd one out because it is just a room below the ground level. The others refer to a house. The maisonette is the odd one out. This is true because both cottage and farmhouse refer to a small house while maisonette refer to a set of rooms in a house.