For heat tape width, it depends on the size of the tub. Most people recommend between 1/4 to 1/2 the width of your tub. I use 6" for my hot spot and am ordering 12" to bump up the temps on the cool side, since my room's ambient temps are not very consistent (they dropped to 72 the other night and I just about had a heart attack). Some people run one big strip of tape through the whole rack, but I like having individual pieces in case of failures or problems with a single level of the rack. Check out the DIY and Caging forums, they're really helpful for building your own rack. There is a bit of a learning curve, but once you've started its a pretty rewarding process.I got super frustrated with mine because it was my first DIY type project ever, but looking back it was totally worth it. Like others have said: Measure twice, cut once. Double check everything! Best of luck to you!