So my son wanted a Quidditch stadium cake for his birthday. I was happy to oblige. I based it partially on this one and some images from the first Harry Potter film. The towers are made of Twix bars. The goal rings are orange gummy rings. The rest of the cake is basic Duncan Hines yellow cake. I had vowed that my towers wouldn't lean, but of course they did. In the future, I'd probably use either a lighter tower structure (Kit Kats or ladyfingers, maybe) or a firmer cake.
In terms of frosting, up until a few years ago I was buying this nice buttercream stuff from a local pastry shop. It was great to work with and very tasty, but it was expensive and had a short shelf life. So I started cheating a bit by using Duncan Hines whipped frosting and pushing it through a pastry bag. That worked okay. Then this year they changed the formula. If you like to use Duncan Hines frosting with a pastry bag, do NOT buy the frosting labeled "Great New Taste! Easier to Spread!" I do not know what sorts of chemicals they used to make it easier to spread (and don't really want to), but it made for a very messy experience. Frosting kept squirting out of the top of the bag, getting all over the table and my clothes. And it made the cake all the more fragile. I'm going with the gourmet crap next time.