i use this in my tort shed. The link is for a roll of it. You can also buy it off the roll in the store, to any length you need or you can buy a precut piece, but that will be the average size of a shower stall. Well worth the money. It will withstand a lot. Most will never have to replace it.
http://m.homedepot.com/p/Oatey-5-ft-x-40-ft-Gray-PVC-Shower-Pan-Liner-Roll-41597/100343454
http://m.homedepot.com/p/Oatey-5-ft-x-40-ft-Gray-PVC-Shower-Pan-Liner-Roll-41597/100343454