Measure and mark 20×20 mm timber into 14 side pieces, making sure each is 25 cm long. To ensure a straight edge use a panel saw and mitre box to cut the lengths. Place one of the side pieces over an offcut of wood and secure to the workbench.
Mark drilling holes on one face of the side pieces, centered on the width and 1.5 cm in from each end. Drill the holes using a 3 mm wood bit. Mark and drill similarly placed holes on the other side pieces, making sure you always drill with the offcut underneath.
Cut a 25 cm square of plywood board to make the base of the support. Mark and drill holes 1.5 cm in from each side at the corners of the square, also using the 3mm wood bit. Mark and drill about 9 evenly spaced holes for drainage, using a 8 mm wood bit.
Use pliers to cut 2 lengths of plastic-coated wire at least 30 cm long. Working from the same side, thread each length of wire through 2 corner holes in the plywood board then pull flush with the board. Make sure that there are 4 equal lengths of wire above the board. Start building up the sides of the box, placing first 2 opposite pieces then the other two opposite pieces until you finish them. There should be 4 pieces on each side of the square.
After threading the final two side pieces, twist each wire end around a pencil to make a secure loop. Cut off excess wire. Finish your box with a non-toxic paint. Choose a color that will match the room you are going to place the box. Fix the hanging chains on each side making sure they are well secured. Now you have a nice and cheap hanging box.