I'm building a woodshed, 8 x 16. Posts will be 4 x 4 or 6 x 6, set in concrete. Floor joists will be 2 x 6's, 16" on center. Floor will be 3/4 ply. All pressure treated. I was thinking 6 posts total. I plan on storing six cord in it. By my calculations, the weight would be 140 lbs/sqft (one cord= 3000lbs; 18,000lbs divided by 128sqft). This should be enough support in the floor, you think?