Warp factor

Apparently I have some learning to do.  Woke up this morning to discover that the floor that I built yesterday for my produce warehouse had warped.  The two outside rows of "legs" were a full 1/4" off the ground.  I'm not sure what caused this, since nothing was painted.  This was nothing more than balsa strips glued to a piece of matte board with CA.  I contemplated ways to fix it, but decided not to waste the time - I started over.

This time, I'm not using the matte board.  I'm building this one the way it would be done in real life, with intersecting cross-beams sitting on the stone piers.  Decking boards (scale 1"x10") will be placed across the cross-beams.

Here's the progress so far, the stone piers attached to the base, and the bottom row of cross-members installed. The second row of cross-members will be placed on top of these, perpendicular to the bottom row.