If you had an unlimited amount of money to renovate/build one room on your home, what would it be?
Only one room. An add on or completely demolish one room and start over. And you'd be responsible for any future financial upkeep, like a higher utility bill, higher property taxes, etc.
I'd have a media room built, with seating for eight (nothing that reclines, no sleeping in the media room!) and I'd have solar panels as a condition of the build because electricity is so expensive here.