It was a 12" square white cake and the hat was a 6" round chocolate cake. Both were two layers, filled with buttercream. The top of the hat was a piece of fondant/gum paste that I made a while ago. So was the "scroll".
Here are the cakes after I crumb-coated each of them in buttercream and covered the square one in my Marshmallow Fondant. You can see the red fondant partly rolled in the background. I draped it over the round cake to become the grad cap.
Congratulations all Graduates!