Very good plans to work from, and very adaptable! I modified the plan to add a sloping lip, which I think finishes the look. I was using old weathered cedar, so I contrasted that with cabinet style joinery (all mitered joints). I like the difference between the old distressed wood and the more refined joints. I set the skill level at "advanced" due to the compound mitered cuts required. I would be happy to supply the miter and bevel angles if anyone is interested.
One small suggestion: I found the diagram of the cuts for the sides to be confusing because the diagram of the piece of wood, which is rectangular, looks slanted in the perspective view. I would project the rectangle flat (all right angles) so that the angled cuts are clearer, and not confused with the "angles" of the sheet itself.
Thanks for a great idea!