I am not an expert by any means but I am building myself a 10 slot rack with belly heat and this is what I plan on doing...
The shelves will be roughly 30" x 17". I will be using 4" flexwatt. 5 Shelves will be for 2x 15 qt tubs and on those shelves there will be one strip of 24"x4" of flexwatt. Therefore for each shelf I need to order 2 ft of flexwatt.
So you order your flexwatt, and if you're doing it on your own, you can follow the directions via the link below to learn how to wire it:
http://ball-pythons.net/forums/showt...148383#1148383
If you're going to order from Reptile Basics, just order what you need and tell Rich what you need done. (for example, I would need 5x 24x4" strips wired.)
Hope this made sense and feel free to correct me if I am wrong about anything. This would also be my first rack build.