1st, You model it's shape like anything else. You probably want to model it with thickness rather than single patch. about 95% transparent with a touch of green or gray.
You can make reflections on glass and car paint more realistic by using a gradient combiner ( leave start and end at 0,0,0) to make a reflection material that makes reflections less apparent for viewing angles that are perpendicular to the surface.
Real glass reflects much more when viewed at an angle than viewed straight on. Same with car paint.