My friend started a remodeling business and I joined him. We would hit the house and start from the ground up. One house had a room addition that was built on blocks so we formed up a foundation. We would take out walls and add headers to strengthen the framing carrying the load. We did it all.
Basic apartment complex stuff. Doing turns and we remodeled
Abused units. We would take everything out down to the studs wiring and all.