You need to do more homework before you go changing an attic into a living space. Mongo already addressed the insulation part - I'll side-step that and move into a different direction.
Attics, when built, unless otherwise specified, are NOT built to be a 'finished space'. With this in mind, the framing is designed to displace the load of the room, and then some. So, by adding a sub-floor, a finished floor, furniture, kids, and who-knows-what-else, you run the risk of having the attic end up in your bedroom! Good luck explaining that to the Insurance Company because they can spell negligence better than I can.
You might want to see if there are any Construction-related books on finishing Basements and Attics. Maybe, at worst, have a Contractor do the 'rough work' and you do the finish work. Also, it's not enough to just insulate the roof. The roof needs to breath! Soffit venting, ridge venting, and soffit chutes are necessary to do this. THEN comes the insulation.
So, you see, it's not as straight forward as you might think. Sometimes, hiring a Pro is money well spent. IMO, this is one of them. My best to ya and hope this helps.