So I am doing this cake for a co-worker, for his son's birthday. It is going to be a tractor for 30 people. I have some ideas, like to set the cake on a raised cake board, with gumpaste tires and details. What I really need help with is what the dimensions need to be. I have no idea how much cake I need!!
So, now that I have been thinking about it, I think I am going to do just a 9" x 13" sheet and then do the tractor on top. But I still need help on how to do the tractor!! Especially now that it is going to be sitting on top of the cake...
Build it in fondant or gumpaste.
Check the gallery or search under "tractor" there is a lot of 3D tractors. You don't have to get so very detailed if you don't want to....check there some great ideas.
I have done Thomas and Dino on a sheet cake.
I made a piece of rectangel/round shape out of fondant/pastilege a week ahead to let it really dry to put Thomas/Dino on it.
When placing Thomas/Dino on the sheet cake I put 3 - 4 big straws underneath for support.
I would probably build a "base" using dowels for the axles and a piece of thin wood for the base of the body of the tractor. Use cake for the body of the tractor and maybe chocolate donuts covered in black fondant for wheels (I love using donuts for wheels!). If you use dowels for axles, you can shove those donuts right onto the dowels.