Select the polygons on the next picture and extrude them 200 units.

In the newly extruded part create a window using the same slice plane technique as before. Next, select the polygons that represent the door and windows on the front side of the house and extrude the by -5 units.

Now switch to the back of the house and slice in some new more windows and extrude them like the ones from the front.

Create some more windows on the sides of the house:

Now we are going to model the roof. Select the polygon from the next picture and delete him.

Select the top polygon and extrude it by 100 units.

Select the 2 vertexes on the top of the mesh, right click on one of them an choose Collapse.