Looking for ideas to insulate an unfinished attached 3 car garage…

Its 768sq foot. With 1 garage door oversized (?10 foot), the other door is a standard 2 car wide garage door.

No "attic" simply open space above the roof joists, roof is 2 story + height over garage. Sloping down to single story over the 2 car door side of garage.

1980 stick build on pad.

? Insulate the entire space

vs insulate just the useable garage space? (Direction I'm thinking) ie ad furring strips to joists to…

Insulating a 3 car garage?