Like Tom I used OSB and didn't paint it. Not painting it saved money and didn't hurt lighting much. I am talking about the shop I used to have and wish I had back. Oh well I guess that is life.Thanks Tom. It may be that OSB is the way to go. It's about $350 for the 1/2" OSB and $515 15/32" PW. Saves me ~$150 that I can use for insulation, paint, or tools.