Hey there!
I actually made my own rock waterfall for no more than a few bucks!
lol It takes time to get it looking how you like it though.
This is a point in the right direct -- YouTube - ‪Part 2: Building A Vertical Dart Frog Vivarium HD‬‏
Watch the video, just remember you have to seal the grout with some clear acrylic or epoxy resin.

Hope this was helpful!

-Kevin

P.S. I highly recommend watching the 4 part series if it is your first vivarium =)