Hi Kevin,
With Rubbermaid and Sterilite discontinuing or marketing new boxes on a regular basis "blueprints" are pretty much useless anymore. You basically to find a box and design your rack accordingly.
My only recommendation in that regard is to avoid boxes with 4 (or 6) tiny "feet" on the bottom. These do not work as well in lidless rack systems.
But back to the point. If you use the "edit-find" function on your browser and check each of the last several pages on this forum you will find some great links. Use "rack" as your keyword.
Are you looking to build a normal sweater box rack for medium sized colubrids or something bigger for ball pythons, etc.?