Lay thinner sheet of plywood on workbench and mark out a 24cm square in one corner. Measure and mark out two rectangles 3.5cm x 24cm. Measure and mark out one rectangle 3.5cm x 25cm. Measure and mark out two rectangles 12.5cm x 10cm, two rectangles 3.5cm x 11cm, plus four rectangles 3.5cm x 12.5cm. Finally, mark out one 24cm x 11cm rectangle for the shelf.