In my opinion, it would be very expensive to side with any wood that's going to look good. Plywood, whether painted or stained, is going to look like exactly what it is. And in outdoor grades it's very heavy, as pointed out earlier. I can't even visualize how one would hang such sheets on the rig, to tell you the truth. And what to do about the seams-?
Even the (perhaps) cheapest/lightest/most rot resistant "lapped" siding solution, 1/4" redwood benderboard, will cost a minimum of thirty cents a foot or so...and since it's only four inches wide you'd have to have a lot of it. Means of attachment is a whole different question.
