@Dannydanbo
Kind of but that's not my whole idea. Its very hard to explain, but I'll try:
I mean that you have the wall of the ground floor and first floor and you have a roof on top of that. The ground floor is just the height of a wall. But that wall extends into the first floor. So a bit of the first floor is half a ground floor wall and then a diagonal roof. If you have dormers on this roof the bottom of the dormers meet the tip of the wall.
I hope my explaination makes sense :).