This is how I make a lot of my car bodies. I start with the corner parts, made by using a cylinder. The sides are made in panels that only have one window. The window is made by making a cutting shape of the window so that I can do a boolean cut to make the panel. The first panel is then copied to make the rest so 5 panels make up the side(the doorway is the same as the window opening but taller). The 5 panels are the joined into one side, the extra points and faces are removed and UV-mapped. Finley the side is copied, moved and rotated 180 degrees.
