Wooden Structure Face Material & Catwalks

What material would you recommend for the face panels on wooden telephone pole structures? OSB, CDX, steel, other?

This sign would be in a pretty dry arid/desert type area that gets quite a bit less rain and snow than most areas of the country, but does get some of each.

Also, are catwalks necessary on a rural telephone pole structure?

My first unit was a wooden structure and treated plywood was used for the faces. That was 5 years ago and they are holding up fine but I would recommend steel, example >>> http://www.theirvincorp.com/BillboardPanelFreeFrames.asp

As far as catwalks go, my first one was built without them and I would say they are not necessary, but they do make things much easier for the installer. If the budget is there I would go for them, if $ is tight you can do without them at first and always add them later.