i've checked some old house to understand how 2level house are..and are almost like an attico but with a little difference. The roof don't hit the floor. There an example more helpful than my words.

In this way you don't need to change the main shape of the mansion or the size, but you'll have a 2level.
The red line is the shape of the mansion how it is now. If you change a little the roof inclination, you should obtain a nice 2th level like the game show.
Tell me if you mind to solve the Attico problem. Imo, it don't care so much :3