Construct the Box. Rip oak plywood into four pieces of the desired column width and height. You don't have to rip them at an angle, since the trim will cover the cut edges. Attach three of the pieces with glue and nails to make a long, threesided box. Cut two pieces of scrap 1" x 1" (or other scrap wood) to a length that's about 2/3 of the ...