The roofer wants to tear off existing roof (only 1 layer of shingles) and replace with 3 tab 60 mph rated shingles.

I regularly save all paint, tile, some 2X4, maybe a bundle of shingles. etc.  

He's saying those prices are too damn high.Replacing the shingles on my 1300 sq ft SFR is about $8000

The subject of putting a metal roof over an existing shingle roof was discussed.

The design life of plumbing is about 60 years, a roof 20-25 (for cheaper shingles typically used on a duplex), carpet anywhere from 3 to 10 years depending on the tenants. 

One contractor says he'll put on a new roof, 30 year dimensional shingles over existing roof for about $6000, using Tamco shingles (http://www.tamko.com/ProductDisplayTest/tabid/53/ControlType/productDisplay/itemid/168/Default.aspx) .

As a Chemical Engineer, I researched my first mold property in 2003 adn realized that there is no official certification for mold remediation - only training classes that allow you to say you are certified and hang your shingle out the next day.

As with Apartment buildings, lead paint, knob & tube wiring, aluminum wiring, flat roofs, asbestos shingles, in ground oil tanks, etc. can all be issues.

I just had my roof and detached garage stripped and re shingled this summer. 34 square is the size, pretty similar to yours.

If you have an 80 year old farm home in the great white north with wood siding and shingle roof it could be double that.