Here are the raw materials for the box. Everything is standard cedar used for fences.
The planter is basically a four sided box, with both the floor and top open. The shell consists of two 2x6's sandwiched around a 2x4. Each long face takes two 2x6's and one 2x4. And the two short edges together take the same material as a long edge, making the total lumber six 2x6's and three 2x4's. An additional two 2x4's were needed for the internal framing.
The separate pieces of wood are held together by 2x2's. I only needed one for the short edges, and used four for the log edges. Everything is secured together with 3" outdoor wood decking screws. A power drill made assembly a snap.