hi jami,
is this castle for a child or an adult? for a child i've used a couple rounds (8in and 6 in) and turned the pointed sugar ice cream cones upside down for the points of the castle and gumdrops, mints, and so on for the windows, doors etc. for an adult (& if you're willing to put alittle time into it), i've used a wilton wedding cake design (simplified for a b-day of course). i forget which book it's in but it was on the cover of one of them, and i also saw it in a different wedding book by wilton. the design on it was pretty elaborate but you can use you imagination to make it easier but still pretty. hope this helps alittle & good luck! dani