You would have to manually draw in the interior facing of the walls. Measure towards the middle of the house the thickness you want the walls to be and then draw them in.
Each face in SketchUp has a white and blue face to represent a “front” and “back”… If the interior faces of the walls happen to show up blue, you can right click them and select “Reverse Faces” to switch them to white.
I hope this makes sense.