Repair of fabricated metal chimney/flue
If it was one of the houses I built in the late '70's, the framing may go down to the second floor. I attached the chase, of T1-11 plywood to 18' studs on three sides, to get the required clearance over the roof surface with the metal chimney, to the exterior wall siding. Then jacked the whole thing upright, with the Fireplace cantilever floor stopping it from going too far. Then set the roof, built the rake chase wall on the trussed, sheathed roof. Hopefully, only the siding needs replacing....
Be safe, G