I did, however, like that they wanted to incorporate felt...that was something I hadn't thought of. So, here they are, our finished cardboard castles. You can check out the rest on our Artsonia gallery!
If I ever do this project again, we'll definitely use the sponge-texture for the bricks instead of painting the brick lines. It was so much faster. I also think I'll definitely make them paint the inside, at least a solid black color. Even though we covered the boxes with gesso, you can still see some of the cereal box print through the primer which I find distracting.