Just make sure the frame is square, otherwise pieces won't fit together properly. Spend a little extra time making the bevel and miter cuts so they line up flush. The height of the shelf depends on the size of the pot you are putting in the planter. Situate the shelf so that the top of the pot is level or a little below the top rim of the planter. This planter box is built around a series of frames screwed together, then covered with siding, which is nailed in place, or you can choose to use either screws or nails throughout.
Decorative trim is added to the top and side.
You can position the shelf at a height best suited to your plant. For the frames, cut 2x2 uprights and 2x4 crosspieces on a table saw. Begin by marking the length on the pieces. Line up the cutting mark with the blade and rest the stock against the miter gauge, and then make the cut. Assemble a pair of frames, each using two uprights and two crosspieces.