A year ago we asked bids to do just that, and one quoted us $35k for a 7x10 which extends our bedroom out to include a master bad and maybe another closet area. We'd have to extend the roof line, flooring, etc, which is why it came out about $500/psf, VHCOL. And our construction friend said we were bid a fair price. We still have to pull the trigger so that's the extent of my experience.