I chose 19" wide for the space I wanted to fill. This dimension will depend on your space and the board you are working with. Trim with miter saw.
Trim a small piece off of the edge of your board. Cut that into 4 equal parts. Glue to the bottom of the original board with wood glue.
Use whatever you can find to create a "worn" look. You can use a sander, planer, hammer, chisel, wire brushes, etc.
Load the riser will all your favorite accents - book, candles, plants, etc!