How to install an jndoor spiral stairs

Why you cannot find direction for cutting the hole is because there are so many different kinds of floors. There is not one correct way.
furthermore it is very likely you will need some kind of support added around the perimeter of your new hole.
---Unless you have a good mechanical sense and do not mind taking a risk, I would suggest you contact an arcatect or engineer

In all honesty,

this isn't really one for the do it yourselfer. i'm a master carpenter, and since your asking this question i feel that you already knew that.

there afre gonna be wiring and plumbing issues certainly, and possibly structural and gas too. so if your not familiar with these other trades at least hire somone to work with if you can find someone.