I was asked to make a "Grave Digger" Monster Truck Cake for a friend at work. It was for his grandson who was turning 5yrs old. He brought me a toy truck to use as a model. This Homemade Monster Truck Birthday Cake Design was the first Monster Truck, or any vehicle cake I have ever done.
I baked 5 single layer 11x9 inch cakes and stacked them on top of each other with a layer of buttercream frosting in between to get the height needed. Then for the base I made a batch of rice crispy treats and covered it in fondant. Remember to let the rice crispy treat cool completely in the refrigerator before you try to use it as a base. Then after I stacked the 5 layered cake I started to carve out the body of the truck. This was kindof messy, so make sure you have room for the mess. Then after the cake was carved, I frosted the entire cake with buttercream frosting. I then covered the entire truck with black fondant. As for the windows, I measured and cut out the windows from white rolled fondant and sprayed them with silver edible spray and used vanilla to stick them to the cake.
As for the flames, I did the same cut them out of rolled out green fondant. the rest of the color like the red, yellow and purple, I used buttercream to finish the decorating. I then used a wooden dowel to keep the cake on the base. I went into the center of the base and up through the bottom of the middle of the truck. This helped to keep it secure. The tires are pinwheel doughnuts dipped in melted chocolate.