All the castle needs now is some decoration. I sometimes use icing left over from decorating the Christmas cake. Fondant icing is good for sticking gingerbread men, trees ...
Step 3: Design stage
Now it's time to discover your inner architect and plan your gingerbread building. If you haven't done any gingerbread construction before, keep it simple. Bear in mind where the building is to be sited, for example if it is to be mounted on a cakeboard, don't make it too big.
My castle is made with 16 tower pieces of 7cm by 20cm and four wall pieces of 14cm by 14cm. I also made four equilateral triangles with 8cm sides for the roof of one of the towers.
Also bear in mind that gingerbread is a temperamental building material. It will often change shape a bit during cooking.