re: Plywood Storage Rollers

A little late to the party but the interesting thing about the design is that because each disk is spins freely, it allows you to slide one sheet out at a time without having the other sheets also on there slide out with it.  That Mcmaster roller you linked to (link is broken but I just search with the embedded part number) would cause all of the sheets to roll out together.  More likely, they would stay put and the rollers would not roll so you would just be sliding the single sheet over the rollers and you might as well use pipe.  If you decide to go with the roller approach, I would buy some cheap bearings and put one or two in each disk/wheel so that they roll very easily. 

All that said, my cart is a copy of the Woodworking for Mere Mortals lumber cart and I do not find that it is that hard to simply slide the sheets in and out from end