I used two 9×13 chocolate cakes, one for the body and the other for the wheels of this garbage truck cake. Froze the cake and then cut in the shape of the garbage truck to match the birthday invitation.
Frosted the entire cake with a thin layer of icing. Froze cake again, then used green and gray frosting for the body. Piped the details on the exterior of the truck. Used the star tip to fill in the fenders, windows, and other areas. Cut three circles of cake from the second 9×13 cake and frosted them black. Used the star tip for the hubcaps.