My daughter wanted a castle cake to go with her Cinderella/Princess party for her 4th birthday. I've never made a "shaped" cake before, just rectangle and round. I got many good ideas from this website, and then altered them to fit my own cake.
I made two boxes of cake mix. Each mix made one square 9x9 cake and five regular sized cupcakes. (I had originally planned to make the cake have round rooms on each of the four corners using soup cans. I had read that on some of the write-ups...it didn't work for me. The cake either wouldn't come out of the can or it fell and was too short and too fragile to stack.)
I purchased a cake tray at the party store and made sure to put wax paper under the 4 edges of the cake before frosting so as not to get the tray all messy.
I leveled the two squares with a serrated knife and then stacked the two squares on each other with frosting in the middle. I frosted the cake with a crumb coat using white canned icing (NOT whipped, just regular. It stands up better to frosting and piping). I made the rounds using 4 of the cupcakes. I cut off the tops of the cupcakes and then cut the top at an angle so it would rest evenly on the cake and not be at too much of a slant. I crumb coated the cupcakes also with the white icing and then used white round Popsicle sticks as dowels so the cupcakes wouldn't fall off. I let the crumb coat dry for one hour.
The crumb coat took almost a whole can of white. I tinted another can pink and frosted the whole cake. I used half of a can and tinted it green for the grass (didn't use all of it). The other half of the can was left white for the words and windows/door. I used a short offset spatula for frosting (works much better at intricate work than the long bendy kind of spatula). I used the spatula to make marks up the sides to make it look like the castle had some depth, and to cover up my inconsistencies in frosting. I used part of a can of chocolate frosting for the middle, but you could probably get away with just 3 cans, I had a lot of leftover.
The BEST part was using the Wilton cake press for the letters. I got it at Michael's and it has backwards letters you put in a tray and lightly press on the cake and then fill with a small tip. The letters looked so professional and I got tons of compliments on my piping.
The spires are sugar cones dipped in melted chocolate and pink and white sanding sugar. I put them on the cake at the last minute just in case gravity would pull them off, but they seemed secure. I got the figures at the dollar store and the Cinderella/prince from the party store. They were attached to the board using icing and then I added green "grass" around their feet for a more realistic look.
Everyone loved the castle cake and my daughter was so happy. It fed 11 4-year olds and 14 adults (small but ample slices).