A cornice board covers up any unsightly blinds or curtain hardware you may have in the window. The board functions as a much more durable valance. Since you attach the board to the wall, it's a little more permanent than regular valances. You can make your own cornice board, even if the thought of woodworking terrifies you. Ask the salespeople at the hardware store to cut the wood to size for you so you can skip sawing it yourself.
You'll need an afternoon to complete the project. Make sure you give yourself plenty of time so you're not rushed. You'll need a wood board that is 6 inches longer than the width of your window. Its height should be 1/5 the length of your window. You'll also need two 6 inch wide pieces of wood, screws, a drill, L brackets, upholstery batting, medium weight fabric and a staple gun.
Attach the two 6 inch wide boards to the ends of the long board. Drill two screws into each end, on the front of the long board. The fabric will conceal the screws when the project is done.
Lay the fabric out on table or the floor, face down. Put the batting on top of the fabric, then the long board on top of the batting. Wrap the ends of the fabric and batting around the board, on the back of the board. Pull tightly, then place a staple in the center of each edge. Continue stapling, spacing them about 3 inches apart until the fabric is securely attached to the board.
Attach the cornice to the wall using the L brackets. Screw two L brackets to the edge of the 6-inch wide boards. Place the cornice above the window. Use a level to make sure it's even. Screw the other side of the L bracket into the wall.