Cardboard boxes large

http://www.instructables.com/id/Easy-Cardboard-Shelves/

http://www.wikihow.com/Make-a-Cardboard-Box-Storage-System

Cardboard shelving does not sound like a very good idea. Cardboard, no matter how heavy the corrugated strength, it will not be strong unless the corrugated tubes are stacked vertical. By that I mean, you could cut 100 2" x 9" pieces of cardboard, with a the corrugation 2" along on the vertical, so the 9" cut would be cutting against the corrugation . Then if you glued the 100 pieces together, flat sides together, you would come up with a pretty strong shelf about 20" long. And then you could put a long 9" x 20" piece of cardboard on top of the shelf to cover the holes of the corrugation.

Thanks