You would really need to go back through the records and find out how much the original property sold for. Using round numbers…

avg new construction… nothing special is around +/- 200/sq-ft.

Arch/Eng ~50K
Permits ~25K +/-
Const. loan fees 10%

So 1800(200) + 50 + 25 + 10% = ~475K in const. costs

Now add in the property acquisition price to that figure.

If the guy bought it in 1999 for 225K he’s sittin pretty

If the guy bought it in 2005 for 650K he’s going to lose his ass.