FROGs (finished room over garage) tend to be cold, I'd definitely upgrade the insulation

Are you familiar with local fire codes for over-garage spaces?

Fire code requires that walls and ceilings of the garage below be covered with a minimum 20 minute fire barrier (1/2" sheetrock on walls and 5/8" firerock on ceiling).

This can be done, but sometimes it requires a heated garaged if one lives in a cold climate and the space is to be used for living. I wish I had one as it is often cold in my library, which sits directly above my basement unheated garage. If it were an outside garage, it would be very cold.

Yep, you'll need to frame the floor above the garage as if an occupied floor (floor dead and live loads), plus frame the roof separately so that there is clear space for humans and other creatures.

Thank you all so much for comments to date - I'm keeping track of all your suggestions

You might want to consider a future bathroom as well. Even if it's a half bath.

How does this all tie in to the balance of the home? The design should all be taken into consideration at the same time in my opinion. How you frame, build, insulate and roof the portion over the garage directlt impacts the rest of the home, no?

Any additional technical comments on modifications required for the flooring and roof system? thanks again!!

Put down 1/2", 5/8" or, better yet, 3/4" plywood subfloor until time to add interior finishes (assumes 16" OC floor joists). Roofing is simple: make it fit, match and shed water, at the outset, like the rest of the roof over your house. Wire, plumb and HVAC the interiors whenever you have the cash.

Screw drive garage door opener and lots of soundproofing on ceiling --clips and resilient channels--plus upgraded insulation.

To follow up on this...If in the base spec was the construction of the garage, what would be the actual spec upgrades that would be incremental (ex., base spec is subfloor can't support weight --> upgrade is subfloor that can support through 16" OC floor, existing insulation --> upgrade is incremental insulation)...ie, don't want to double count specs....apologies if this is convoluted