Measure and cut three 14-by-14-inch and two 14-by-13-inch pieces of plywood. Use a high grade of plywood for durability and a professional appearance.
Match the ends of two 14-by-14 pieces with the 14 inch sides of the 13-by-14 pieces and glue with wood glue. Clamp it together while the glue dries. Use five nails to secure each edge on the top and bottom of the cube after the glue is dry. Countersink each nail so it sits slightly below the surface of the wood.
Place the remaining 14-by-14-inch piece of plywood onto the back of the box and secure it with glue. Use five nails on each side to secure it after the glue is dry. Countersink each nail so it sits slightly below the surface of the wood.
Fill each nail hole with wood putty, using a putty knife, and let it dry. Sand the box until it is smooth. Paint the cubby a color that will match the decor of the room you will place it in. Wait until the first coat is dry, and add a second coat if necessary.
Secure the cubby to the wall by holding it in place and drilling through each of the four corners of the back panel and into the wall. Use 2-inch screws fitted with washers to secure the cubby.
Repeat Steps 1 through 5 to make additional cubbies to mount below, above, or next to your first cubby, if you desire additional storage.