Mar, Apr, May, Sep, Oct, Nov
Mark and cut all the pieces of timber to the correct lengths, cutting the ends as squarely as possible for a smooth finish. Using a 3mm drill bit, make a hole around 2.5cm from the end of every length to stop the wood splitting when you put in the screws.
Lay out two 100cm, 60cm and 40cm lengths to form the frame. Butt one end of each length up to the next with the drilled holes on the side. Check the angles with the try square before fitting a screwdriver attachment and fixing the frame together with 7.5cm screws.
Cut treated gravel board to the appropriate lengths for the planter bottom. Place the bottom boards on the frame. Don't worry if there are gaps up to 5cm wide between the boards as the planter will be lined. Pre-drill the bottom boards, check the frame is square again, then attach the boards to the frame using 5cm screws.
Flip the frame over onto the other side so the bottom boards sit on the ground. Lay the next course and alternate the corner joins. Check all ends are flush and fix with 7.5cm screws.
Build up four layers in this way. Instead of a final 60cm piece, lay a 100cm length across the gap to support the raised square.
For the perfect fit, measure the cross-bar piece when it's in position across the frame and cut it in situ.
Attach one end of the length with a 7.5cm screw from above, as shown. Fix the other by screwing into it from the outside of the frame.
Lay the 45cm length across the other gap, lining it up with the adjacent side to make a rectangle (see picture). Check the angles and screw it into place.
Finish this layer by placing two 40cm lengths at right angles to the 45cm piece, then cut the final length to fit the remaining gap. Continue adding courses of 40cm lengths of timber, with alternating joints, until the raised section of the planter is four layers deep.