Looks like you have intersected from the context of the roof which has put the geometry of the walls there. As you don't need it it can be removed.
Your walls are raw geometry and are reversed. So select them all and choose reverse faces, then select them all and choose, Intersect with Model. Then remove the excess geometry.
I've also assigned the Roof group to the h roof layer so it can be turned on and off.
Follow along in the gif.
Intersect house.gif