My son wanted a green Mack truck cake for his 3rd birthday.  I made a 9 x 13 rectangular chocolate cake.  I cut 2 long rectangles and stacked them and two squares and stacked them.  I carved the semi to the correct shape.  I covered the cake with a light layer of butter cream frosting.  I placed rolled out green marzipan on top. Some of the decorations are made of gum paste and some are pre-cut sugar sheets.  I also used edible marker to draw on the gum paste.  The wheels are mini Oreo’s.