Obviously the first ingredient you need to get together for cheesy potatoes is some potatoes. They're supposed to be all shredded and whatnot. And you need like, some amount. Half of a 32oz bag, which is 16 oz, which is.. some number of grams, if you're metric. I don't remember now, though. You have the internet, go look it up, you lazy bastard!
Of course, it goes without saying that you could buy actual potatoes and then go to all the trouble of peeling them, and shredding them, and getting the excess water out, and blah blah blah. I'm a busy guy, so frozen is good enough for me.