The most important parts of your set up are going to be heat and hides. Don't use the mesh or wire screens they sell as tops to reptile cages that will let all of your heat and humidity (or you'll end up covering up with a towel and wondering why your snakes not shedding right). Get an Under Tank Heater, as balls need their belly heat to help with their metabolism, the UTH do a pretty good job at keeping the ambient temps up. I would skip the ceramic or light type heaters as they dry out the tank. I have one and use it just on really cold nights but I make sure to mist the cage first. Hides are important, I put them the hot and the cold sides. This is where your snake is going to be spending most of his time and are his safe spot. You can use anything from a plastic dish to a shoe box. Start small (about the same size as your snake in a relaxed ball) and get them bigger as the snake grows. A water dish that does not tip over is good. You can us any type substrate: newspaper, aspen, cypress, reptibark (don't use sand or anything with cedar). One good sturdy branch is usually enough climbing aparatus for balls as they are primarily terrestrial. Invest in a good digital thermometer/hygrometer (the analog ones aren't very accurate. And I think that's about it. Here's a picture of my tank, I'm actually cleaning it out today so this is an old picture it's changed a bit. Hope this helps!

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Tosha 
3.7.0 Ball Python (Harry and Fluffy and currently un-named)
0.1.0 Siberian Husky (Kita)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Dessert Tortoise (Pope)
7.9.5 Fish (1,2,3,4...)
0.0.1 Frog rescued from pool skimmer
0.0.2 Lizards rescued from pool skimmer