It's not fine art, but it's a functional and cheap planter using no frills and the minimum of expense and effort. All good points, in my view...

Ingredients for this main course are...:

6x rough-sawn planks (2400mm x 100mm x 10mm) - that's 2 for each long side, 1 for the ends, 1 for the bottom.
2x 2400mm stud lumber - 3x2 and 4x2) for the corner legs
1 x 2400mm 3cmx2cm for the bottom rails
Plastic sheeting
Soil and whatnot
Loads of screws

Hope you enjoy making your own!