Form the corner of one planter box. Place the edge of one 2-foot-by-2-foot plywood or cedar sheet against the face of a second 2-foot-by-2-foot plywood sheet. Make a right-angled L-shape with the two sheets to form the planter box's corner. Hammer in one 4-inch nail every 3 inches along the joint to create a tight seam.
Attach a third 2-foot-by-2-foot sheet to the second sheet to keep the planter box even. Hammer in one 4-inch nail every 3 inches along the joint of the second and third boards to create an even U-shape with right angles.
Place a fourth 2-foot sheet at the top of the U-shape to complete the frame of the planter box. Attach the board with 4-inch nails at both sides. Hammer one nail every 3 inches.
Add a fifth board to one open portion of the planter box to give it a bottom. Hammer one 4-inch nail every 3 inches along all four sides of the planter box to secure the board.
Create one more planter box with the remaining 2-foot sheets. Follow the same procedure you used to create the first planter box.
Attach one 4-inch-by-4-inch plywood post to one corner of a 4-foot long plywood or cedar sheet. Place the plywood post so that it aligns with the corner of the sheet, and attach it with 4-inch nails. Hammer one nail through the plywood or cedar sheet at each corner of the plywood post.
Connect three more plywood posts to the 4-foot long plywood or cedar sheet. Attach one post to each corner, using the same procedure you used previously.
Attach one planter box to a 2-foot end of the bench. Connect it to the bench and the legs of the bench with 4-inch nails, hammering one nail every 3 inches along the top portion of the box and down the legs to keep the planter box firmly in place.
Connect the second planter box to the other 2-foot end of the bench. This scomplete the planter bench's construction.
Apply a non-toxic, weather-resistant stain to the planter bench. That will ensure the wood can withstand weather and water. Allow the bench to dry for 48 hours before adding soil and plants to the planter boxes.