On tear offs we start by laying tarps on the ground, covering windows, plants, etc. with plywood, placing boards above the gutters to protect them, we only tear off as much as we can clean up, felt and roof back in any given day. At the end of the job we run a magnet around your home to pick up any leftover nails. On the average, house labor & materials start at $180.00 per sq for 3-tab shingles and $190.00 per sq for dimensional shingles. Flashing, wood work, etc. is extra.
When replacing an existing roof on an older home tearing off the shingles down to the decking is the best way to go. This way I can inspect the decking for signs of leaks and other damage. Then I can start from scratch to assure you get a worry free roofing system.