I suppose you could print small panels and glue them together, but it would look more like a tile floor than a car body. If you want to make big, strong, smooth contoured panels like most car bodies require, use a CNC router to machine urethane foam into the shapes required, then coat them, sand them out, apply mold release, and lay up the panels in fiberglass and resin, or a similar composite system like epoxy and kevlar. This will be stronger, cheaper, and better-looking than the method you're proposing.

Andrew Werby
www.computersculpture.com