Cut two 12-inch-long pieces for the ends and an 18 1/2-inch-long piece for the bottom from a 1-by-10 inch board.
Cut two pieces the same size as the bottom using a 1-by-4 inch board.
Measure 2 7/8 inches from the top corners inward of the end pieces and mark this point. Mark a second point 4 1/2 inches up from the bottom corners. Connect these with a ruler and cut along the lines to make slants for the end pieces.
Measure the center of each end piece at the top and measure slightly under 1/4 inch on each side of the center mark. Make a line from each of these points that extends down 2 inches. Connect them with a straight line at the bottom.
Cut out the groove you just measured. Cut a handle from a 1-by-2 inch board that measures 20 inches long. Use sandpaper to sand the groove bigger until the handle fits in firmly. Glue it in place with wood glue and let it dry.
Nail the sides onto the toolbox, using wood glue if needed to reinforce them. Nail the bottom on after the glue has dried, if you used glue. Use small nails to reinforce the handle if needed.