Set a 3/4-by-10-by-12-inch plywood board on the working surface to be the bottom board. Position two 3/4-by-6-by-12-inch plywood boards on their long, thin sides on top of the bottom board, parallel to each other with their outside surfaces even with the edge of the bottom board.
Set 1-inch metal L brackets on the inside of the drawer, up against both the bottom board and the side boards. Mark the position of the bracket screws. Drill out each bracket screw hole. Fasten the brackets to the boards with 3/4-inch wood screws. Hold a 1/2-by-1-by-12-inch board across the open front of the drawer, about one inch below the top of the side boards. Drill a hole through this board, which is the railing, and into each side board. Attach the railing to the side boards with 2-inch wood screws.
Hold drawer runners against the outside surface of the side boards. Mark the locations of the screw holes. Drill out each hole and attach the runner with 3/4-inch wood screws.
Position the drawer underneath the cabinet or shelf. Place a 3/4-by-8-by-12-inch plywood board on either side of the drawer. Remove the drawer and position metal brackets between the plywood boards and the underside of the cabinet or shelf. Mark the bracket screw holes, drill them out, and attach the brackets with 3/4-inch wood screws.
Reposition the drawer within the boards and position the other half of the drawer runners. Mark the screw locations for the other parts of the drawer runners on these boards. Drill out the screw positions and attach the runners with 3/4-inch wood screws.