I covered both the 6 inch and the 9 inch cakes in buttercream (both are filled in the middle with buttercream as well...bake two cakes in each size and put them together). I had to use about half a bottle of Wilton red to get this color :). Black was similar too..though if you started with chocolate frosting for the black, you wouldn't need as much color. After I frost the cakes I let them sit for about 20 minutes to allow the meringue powder to do it's thing (1 Tbsp meringue powder in a 4c of powdered sugar frosting recipe) and crust over just slightly, and then I roll over the cakes with my high density foam paint roller in order to get a smoother frosting.
Next I cut out the fondant shapes for spidermans head and face by first tracing it onto parchment paper and then placing it on the fondant and cutting around the parchment.
For the spiderwebs, I used a ruler to make light indentations so everything was even and uniform. Then I went over it with my black buttercream and tip number 3.
Next I rolled out the black fondant, traced out a city, cut the city into about fourths for easier transferring and then 'glued' it onto the side of the 6 inch cake with a little bit of water and frosting. I stacked the cakes and then rolled out a little white fondant.
I was pleased with the way it turned out and so was Ethan which was the most important thing! Overall, it took me about 6-8 hours which included baking, cutting, making and coloring frosting and fondant and decorating.