I have built a few over the years and used Canexel that nail directly onto the studs that I spaced at 16".
None have failed to date and stand up to the elements very well.
I even ripped the Canexel into 3" or so strips to cover the corners rather than special corner material.
For the interior I like metal roofing material for the bottom area (like 36-39" wide) followed by composite or plywood for the top half.
The metal lower since washing etc will deteriorate any wooden product.
For that matter with bottoms protected a guy could even use plasterboard for the upper section other than it is hard to hang tools etc on plasterboard.