I’ve gotten several rough estimates in 2019 from several design and build firms in San Diego to build a 4k sq-ft house from an existing 1100 sq-ft SFR and they came in anywhere between $185/sq-ft on the low end to $350/sq-ft on the high end. Assuming 2020-2021 was/is a fluke in term of material prices, I’d expect us to get back there once supply for materials free flow again.
One have to also remember that there are fixed costs regardless of how big/small you build. So, $/sq-ft will increase from the numbers I stated above if you build smaller.
