I found this amusing, the author goes into how to flatten out a PVC pipe so that its a sheet that can be cut on. Me…I think I would just buy a sheet at Home Depot. But in desparation, or lack of cash, this would be a good workaround (oh and you have time on your hands).
http://www.instructables.com/id/Recycle-Old-PVC-Into-Flat-Sheets/