Measure the dimensions of the top of the toolbox. Mark matching dimensions on the piece of wood from which you make the lid.
Cut the outline of the lid using a miter saw. Follow the pencil marks.
Position the lid on top of the toolbox. Secure the lid with masking tape.
Attach the wooden lid to the rear of the toolbox with T-hinges. Screw the appropriate sized screws through the mounting holes on each T-hinge. Space the T-hinges evenly apart, making sure there is one T-hinge near each edge.