Also, some people use tileboard, which is a tub-surround material that looks like tile and has a waterproof coating on one side. It's pretty inexpensive. You just need to make sure to caulk around the edges with silicone.
You could also probably use those self-adhesive vinyl tiles.
Ceramic tile would probably be overkill (and VERY HEAVY). I tried that (ungrouted, just laid in a cage) once and it didn't work well. Grouted and set, it would make for a very heavy hard to move cage, though I'm sure it would be waterproof then.
A shower curtain would be hard to manage, I think. You might even want to try vinyl contact paper, though I don't know how long that would last on a cage floor (I know people have used it on cage walls/ceiling before though).
-----
Lauren Madar
www.ophidiagems.com
1.1 Hog Island Boas
1.1 Hypo BCI
0.1 Sorong-type GTP
1.0 Normal Ball Python
1.1 Surinam BCC