This project is a rough-hewn window box with a bit of cabin-like joinery on display. The material is cedar with one rough side, a material that is usually about 7/8 in. thick. For a more substantial result, you could use 2-by lumber instead.

To ensure against mistakes, make the box first, then cut the corbels to fit. The face and back overlap the sides by 1-1/2 in., in keeping with the style. The corbels in this installation are mostly decorative (though they do add a bit of support), but the box is actually attached at its back. If you need to attach via the corbels, use very long screws to attach the corbels to the wall.