My son Isaac loves Harry Potter. So for his 10th birthday we had a Harry Potter party. For his cake he wanted a castle. The bottom tier was one and a half 9x13 butter cakes, the second tier was two 8 in round chocolate cakes, and the top tier was two 6 in round strawberry cakes. I covered each layer in buttercream and added blue gel icing for water around the castle. I used a graham cracker for the moat, sugar wafer cookies around the round tiers, and sugar cones for towers. I also added Hogwart's crest on the top tier. It turned out really good. Isaac and all his friends thought it was really cool.