They do make full preasure treated plywood, but your getting into the $25 per sheet range. CDX plywood is C quality loooks on front, D quality looks on back side, wit eXterior glue. Its not ment to gwt wet over and over because the wood isnt treated, but its not the end of the world if it gets rain for a few days before you dry in a roof. If its in a garage, I would expect no problems for many years at around $10 per sheet for half inch, around $13.50 for 5/8ths. The exterior paint with extend that even more. One thing to keep in mind, if your worried about moisture wicking up from concrete slab you can simply keep the bottons about 1/8th inch off the concrete by shimm ok ng the bottom up with a nail as a spacer as you screw it off. I highly recommend using screws instead of nails so you can take panels off to add outlets, compressed air lines ect with little trouble.