10. On the inside of the panels, screw a batten along the bottom edge between the corner posts.
11. Before assembling the frame, mark out for the chamfer detail on the top of the four corner posts. Use a marking gauge to divide the end of the post into an even pattern.
12. With your sliding bevel set to 20°, mark the chamfer on all corners around the post.
13. You should be able to cut close to the line with a saw to remove most of the waste.