This planter took me approximately 90 minutes to make: The design is simple, and so is the required level of woodworking skill, the only tools required are a square, pencil, electric/cordless drill and suitable spade end drill bit, and a tenon saw; although a chisel and some sand paper would be useful for tidying up the slip joints.
I cut down some 2.4 metre long pallet deck planks that were 9 cm wide and 1.9 cm thick to 1.9 mtrs long for the base tier so that the tier inside the slip joints is a 1.8 mtr X 1.8 mtr square.
Only the slip joint slots at the corners of the lower tier need to be half the plank's width in depth, this is to allow all four sides to sit firmly on the ground. All of the remaining slots used in this planter have been set at a depth of 1/3rd of the planks width.
Note that that the 1/2 depth slot is 5 cm from the end of the plank, and the 1/3 depth slot for the second tier is 20 cm in from the inside edge the first slot:
It is important to remember that on all the slip joints you are working inwards so that you keep the dimensions and the slots in the correct place.