yea SketchUp is a good program, but you can still model cars
if you go to google and type in "3-D warehouse" there should be a site at the very top with a whole bunch of different models, go to the search bar and type in "car" or something and there are some preaty wild ones out there, like an SLR mclaren with the door up and you can into the interior.
nice building too!
you could do the interior easily if you wanted to
just make those windows transparent and create some more squares underneath or even import some BMW models that other people have made from that google 3-d warehouse.
If ya need to know how to do that, ill tell you