I'm covering the exterior walls of my garden shed with cedar shake shingles (to match the house) but on the 2 walls against the fence (not visible) I'd like to reduce cost and labor by using some other material. 4x8 sheets of something INEXPENSIVE and paintable would be ideal. The shed is sheathed with 1/2" OSB over 2x4 studs on 16" centers so I don't need structural strength. Any suggestions would be welcomed.