Build a frame for the headboard. We used scrap wood for the header, sides and bottom of the headboard, and a piece of beadboard for the back. Fasten the frame pieces to the beadboard from the back so the screws don't come through the front of the wood.
Before fastening the bottom piece onto the frame, do a dry-fit layout of the of picket fence pieces to make sure they fit horizontally so you won't have to make any lengthwise cuts. Remove the picket fence pieces and then screw the bottom board in place.