I usually ask my children (5 total) what kind of cake they want for their birthday. For my oldest son’s 13th birthday, he picked a homemade skateboard birthday cake.
I got the idea from looking at other cakes. I have been teaching myself how to make cakes, and it has turned into a hobby. I also took a thick poster board and drew more skateboard logos around it, so that the cake was surrounded by logos. He loved it!