Heehaw,
It really makes you wonder about the quality of the treatment process sometimes. I had to sort through a bunch of 5X5 posts just to get a dozen or so decent ones. You know, just about every new deck around here I see built has CCA posts which makes me wonder about how long they will last. I guesss putting them on concrete footers helps the rot problem considerably.
Paul, my grandfather had a Butler machine shed constructed now 21 years ago. It's all steel sitting on concrete footings. That thing is still solid as a rock. I don't know if they make barns in the size you want but it may be worth checking into. I've thought about a steel barn next time, eliminates the structural rot/termite problem.
Grant