This Homemade Castle Birthday Cake could've been much easier than it was...lol..make sure you've got the right pan sizes so you don't have to improvise. Frosting cut edges is no fun.
Several days in advance, either make marshmallow fondant, or get some store bought fondant. You need 2 paper towel rolls, 2 toilet tissue rolls, and one paper towel roll cut in half for the towers. Add black food coloring to a big ball of fondant and knead til even color. Roll out to about 1/8 inch thick, wrap around paper rolls, seal with a little water and using a clean, dry towel, rub smooth. With a sharp knife, carefully make indention all the way around towers in straight lines, evenly spaced, all the way to the bottom. Then make small vertical lines, unevenly spaced. (To make a brick type pattern). Using a paint brush and black color, paint small window openings on the towers. Set towers aside to dry for several days.
I molded the dragon out of fondant as well. Wings and fire were fruit rolls and craft wire. Castle drawbridge was fondant, shaped and left to dry on slightly crinkled plastic wrap, (to make 'wood grain'), then painted with brown food coloring.
You need some height with this cake. I used 3 10 inch square layers for the bottom, (layers were about 2 inches high each) and I used 2 layers for the top (cut from a 13 x 9 inch pan into roughly 6 inch squares, each layer about 3 inches high.)
I used a moist, sturdy sour cream orange cake, frosted with orange vanilla buttercream. Fill and stack your layers and give a nice crumb coat.
I used a few drops of black food coloring added to my frosting to make a good gray. Frost cake all over, and don't worry if it isn't super smooth. Use same technique as for towers to make a 'stone' look to the castle. Take large marshmallows and using your fingers, rub small amounts of gray frosting on them, place around top of each layer of castle for a 'crenellated' effect.
Press drawbridge into front of castle. (I used small balls of slightly flattened gray fondant to make 'stones' and stuck them with a dab of frosting around the drawbridge.)
Rub a small amount of frosting onto bottom of each tower and place around castle. Take sugar cones that have been sprayed with black air brush food coloring and press onto top of each tower.