I used hat boxes that I had purchased at my local craft store. If you are interested in making one, you can find the instructions in my October 2009 blog post.
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Here is the cake in action at the Quinceanera.
This is the before picture, I used Taping Compound (from hardware store) for the frosting. It's in powder form and when mixed with water it looks just like real frosting and spreads on just like the real thing too and it dries rock hard, at which point you can brush paint it or airbrush it. I simply gave it one coat of white Gesso.
Here is the top view of the cake, before and after.