see:

http://www.trylock.com/

these guys do my flat roofing and my pitched roofs they come
recommended to be and now by me for years.
if you tear off all the old crap and dispose of it yourself with a
permit into a dumpster or and repair or replace the the sheathing and
eaves and fascia wood and put in a properly pitched roof in your
climate's zipcode with desired or required railings and gutters and
downspouts, with excellent workmanship, what is it worth is the
question. if you want that roof to last 20 years it's probably worth
$100/year.
we found this company by asking who put in a flat roof at davis
plumbing supply, and lou told me about try-lock. he said it took him
years to find a good company to fix his flat roof problems.