I baked the cake in a flimsy aluminum pizza pan that I found in the baking aisle at the grocery store. I was ready to make another cake in a regular pan if needed but it worked great. (Bonus - no cake pans to wash!)
We added some red frosting for the pizza sauce but that color in frosting is always kind of a let down. Unless you're willing to dump a TON of the coloring in - which tastes really terrible - it always comes out a little bit orange-red. We were able to fix that a little bit by putting the cake under the broiler for just about a minute. The heat helped deepen the color and make the frosting look more like sauce.
Ben cut up little bits of black licorice for olives, we reshaped vanilla tootsie rolls for mushrooms, and used a circle cookie cutter to make fruit roll ups look like pepperoni.
Then we grated some white chocolate over the other toppings and put it into a cardboard pizza delivery box before dropping it off at the school.