Stand 0.5-by-18-by-36-inch side boards on their long, skinny sides. Arrange them parallel to each other. Set a 0.5-by-24-by-36-inch cabinet rear board on top of the side boards. Move the side boards until their outer surfaces are even with the ends of the rear board. Use the drill to make holes along the edges of the rear board, about every 6 inches. Make the holes down through the rear board and into the side boards. Connect the boards using 1.5-inch wood screws.
Place the cabinet with its front surface against the floor. Hold two 0.5-by-18.5-by-24-inch boards against the open sides to serve as the top and bottom of the cabinet. Line up the edges of the cabinet with the edges of the top and bottom boards. Drill evenly spaced holes every 6 inches around the edge of the top and bottom boards and into the side boards. Fuse the boards together using 1.5-inch wood screws.
Rotate the cabinet and set a 0.5-by-24-by-36-inch board against the front of the cabinet. Determine the best location for two evenly spaced hinges. Mark the location of the screw holes on both the side board and the front board. Drill into all the markings, being careful not to break through the front of the cabinet. Attach the hinge to all locations using 0.5-inch wood screws. Test the door by swinging it back and forth a few times.
Clean the surface of each cabinet by wiping it down with a cloth, then washing it thoroughly. Allow each cabinet's surface to dry.
Apply grout to the side of the cabinet, using a trowel, until the grout is a quarter-inch thick. Allow the grout to harden for a few minutes until it's tacky but no longer too wet. Begin setting the mosaic tiles or marbles into the grout by holding them in place for a few seconds before releasing them. Arrange the tiles and marbles until the panel has been completely covered.
Remove any excess grout from the tiles or marbles, using a scraper. Allow the grout on the tiles to dry overnight to ensure a strong bond before using the cabinet.