Making a cornice board yourself is not that difficult. Start off by taking note of the measurements. Then, draw an outline of the rectangular shape on a wood panel, according to the dimensions you recorded. Make sure to add a few inches on either side. This will be the front piece of your cornice board. Use a jigsaw to cut it. Once you have cut it, sand the wood so as to give it a smoother finish. Afterwards, cut the sides of the cornice board. Attach them to the front panel with glue and then secure with finish nails. You could either paint your cornice board or cover it with fabric to make it match the curtains.