Game Development Reference
4. Once you've finished, you should already have the following basic car shape. You
can now hide the images to see your model beter.
5. Now to finish off, extrude the plan shape and again use Intersect with Model .
Delete the parts you don't need.
If you have SketchUp Pro you can do this much easier using the Solid Tools.
Here's how. After extruding each part, turn it into a Group .
Select your three groups. Then simply go to Tools ¦ Solid Tools ¦ Intersect .