The first step is to make a template of the side view of the car, and cut a board that will support the cake. I base the length of both on the length of the cake pans that will be used to make the cake.
Stack the cakes and use the template as a guide to cut the shape of the car out.
Cut out notches where the tire slots are located.
Crumb coat the cake, then cut out some fondant or gumpaste to cover the cake where the windows will be.