House is a shell. However, preliminary design set is complete. Permit drawings are near completion but buyer still has the opportunity to make customizations. Furthermore, current foundation walls do not have footing. Increase in loading would be addressed by beams and posts that are to be supported by new spread footings. Floor of basement to be lowered using benching or underpinning. (Current plans opt for benching). Current plans are for 4600 square feet of finished space to include 6 bedrooms, 4.5 baths with an in-law suite, plus a rooftop deck and a 2 car garage and a dugout basement. So do your ARV estimate based on the above information.