Keep in mind too that you want it so that it's easy to clean. I used to have fancy elaborate cages, but it got to be a pain having to clean everything. Now it's just a simple silk vine that goes across the bottom for me.

As for using flexwatt inside the cage. What I would do is put down the flexwatt, then put down a piece of plexiglass to cover it and completely seal the edges of the plexiglass using silicone. You want the flexwatt to be waterproof incase your snake manages to tip the water bowl over; this will prevent electrocution.