Determine the dimensions of the toy box bench based on your storage needs and space requirements.
Measure four sections of 2-by-4-inch lumber to the width of the toy box bench, and four sections to the depth, using a tape measure. Cut the sections to length with a circular saw. Miter the ends of the lumber sections at 45-degree angles with a miter saw.
Assemble two width and two length sections into a rectangle to form the base of the toy box bench. Insert 4-inch wood screws through the corners with a drill equipped with a screwdriver bit. Repeat this process with the remaining length and width sections.
Cut four sections of 2-by-4-inch lumber four inches shorter than the height of the toy box; these sections form the posts of the toy box. Turn the frames on their 2-inch edges and place one of the posts at each corner. Insert 4-inch wood screws through the frames into the ends of the posts.
Turn the assembled toy box frame upright. Cut two sections of 2-by-4-inch lumber to the height of the bench back. Attach these sections to the back of the toy box on each side.
Measure the interior distance between the bench back posts. Cut two sections of 2-by-4-inch lumber to this distance. Place one section flush with the top of the bench back posts and secure it with 6-inch wood screws. Repeat this process with the second section by placing the bottom edge flush with the top of the toy box frame.
Cut sections of 5/8-inch-thick plywood to fit the front, bottom and sides of the toy box, and to fit the interior dimensions of the back of the toy box, using a table saw. Attach these sections using 4-inch wood screws.
Cut a section of 5/8-inch section of plywood to fit the bench back. Attach the plywood section to the bench back frame with 4-inch wood screws. Cut an additional plywood section to fit the top of the toy box.
Set the top section on the toy box. Attach a hinge at each end with the included screws.
Sand the plywood surfaces with a palm sander to round the corners and smooth the surfaces. Paint or stain the toy box bench as desired.