What sized cakes should I use to make a 3D football helmet cake?

I use 10" rounds. 3 of them.

depends on how many servings you need/how big you want the cake to be. i recently made a true to size helmet and used the actual mouthguard from the real helmet as the mouthguard on the cake, so it had to be to scale. plus, they needed about 40-50 servings. i used 5-10 inch rounds (each of my layers was about 2 inches). i put two layers down, put bubble tea straws in, then the top 3 layers were on a cardboard round on top of those. then i just starting carving while using the real helmet as my guide.
the pic is in my photos

will this help


http://cakecentral.com/cake-decorating-ftopict-615967-.html