Click "File," then "Open" to load the 3D building project in the SketchUp software.
Use the "Pan," "Orbit" and "Zoom" tools to position your camera on the wall to which you would like to add thickness.
Select the "Push/Pull" tool from the toolbar. This looks like a box with an arrow coming out of it.
Hover your mouse over the outside or inside face of the wall. The program will highlight the shape's face with dotted shading to show you which wall you have selected.
Click and drag the face of the wall outward using your mouse. This will increase the thickness of your wall.
Release the mouse button once the wall has become thick enough.
Repeat the process on all walls to which you would like to add thickness.
Save the changes to your 3D project once you have completed your edits.