This beautiful wall shelf is basically a 1x4 or 1x6 board with crown molding mounted on the bottom. As shown, you cut the crown molding returns to return to the wall as well as finish the edges. Dress the edges of the shelf board with a router as desired. Sand, stain and finish.

The size of the crown molding you choose will determine the size of the shelf .  Mount this on the wall by cutting two grooves in the back.  Locate these grooves on the bottom of the shelf portion. Mount on wall with nails or screws that fit into the grooves.     Simplicity is beautiful.