Lay a 3/4-by-15-by-25-inch piece of plywood flat on the work surface and bead a line of wood glue along the 15-inch ends. This is the toy box base.
Abut two pieces of 3/4-by-15-by-15-inch plywood onto the ends of the base at right angles, flush with the bottom of the base. These are the short sides of the toy box. Square off the short sides then clamp them in place to dry for an hour.
Secure the short sides to the base of the toy box with flat head nails hammered through the glued joints every 3 inches. Unclamp the short sides.
Bead a line of glue along the 25-inch edge of the base and the short sides as well. Abut two pieces of 3/4-by-15-by-26.5-inch plywood at right angles to the base. These are the long sides of the toy box. The ends of the long sides will form right-angled corners with the ends of the short sides of the box.
Square off the long sides of the box then clamp them in place to dry. Secure them with flat head nails through the glued joints at the base and the short sides of the box. Unclamp the long sides once they're dry.
Position two pieces of 1-by-2-by-25-inch lumber over each short side. These are the backrest arms of the bench toy box. One end of the backrest piece should be positioned in the center of the short sides. Angle the backrest arms backward so that it lines up with one top corner of the short sides and clamp them in place. There will be approximately 15 inches of backrest arm protruding at an angle above the box.
Secure the backrest arms to the short sides of the box with 1 1/2-inch wood screws driven every 3 inches through the backrest arms into the side of the box.
Insert a piece of 3/4-by-7-by-26.5-inch plywood between the backrest arms. This is the backrest, and it should be positioned straight, not angled. The backrest should be roughly 3 inches from the ends of the arms. Secure the backrest to the backrest arms with two wood screws driven through the side of the arms into the abutting backrest.
Sand the toy box bench, including the 3/4-by-16.5-by-26.5-inch piece of plywood, which is the box lid/seat. Paint the box and lid in the desired color(s).
Center a 24-inch long piano hinge over one long edge of the lid and secure it in place with 1/2-inch screws through the screw holes in the hinge.
Center the lid over the box, with the hinge at the back. Secure the remaining half of the hinge to the back of the box with 1/2-inch screws to finish your bench toy box.