For the next step, we will add a roof and a window and set a wooden texture on the floor and a glass window. Start by using the rectangle tool to enclose the roof. Then draw a rectangle on the wall of the left hand side and use the push / pull tool to push the rectangle through to the inside. Delete the paper thin wall that is left and you should have a window hole like so:

Our box room with a window and a roof.

As a final step, use the Move tool to put Derrick somewhere side the house.