BOATBOB2 has the right idea. This s how I work out these things on paper.
Get the side photo...enlarge it on a copier....then take another piece of paper and lay it over the photo to do a tracing. (a light table helps but you can tape it to an outside window and get enough light thru it to do the tracing.
Trace the outline of the car, the windows, and any other important lines you need. Leave out the stuff you don't need.
Make that tracing and you'll have a simple line drawing.
Make about 20 copies of that line drawing...and then with an Xacto knife you can cut the roof off, and begin to place it where you think you want it.
You can cut chop and section all the paper pieces, and when you get the shape you want you see the blank spots that need to be filled, as well as all the "challenges" involved.
Good luck!!!!!!! Sounds like a project.