if you decide to giant tarp the roof you have to leave holes for pipes
and chimneys.

flat roof? a flat rubber roof may want a latex coating each 5 years.

low spot where puddle freezes on flat roof and caused roof damage?

got trees? gutters will block with leaves or ice that will back up and
sneak water above your edge flashing and into the house. what did you
notice when you cleaned the gutters each year?

got gutters that drip on the ends? may be time to fix roof and gutters
must be removed and repitched and replaced to deliver toward downspout
as required in your area.

maybe you have downspouts into the sewers or wherever you send the
water that will clog or break at the trap located under house or under
ground causing gutter backup problems at roof.

is bathroom in-wall exhaust fan exhausting directly thru wall? its
flashing no good or needed recaulking?

some warranties might be worth more printed on tarpaper.

see also the company we hired for our roofs:
http://www.trylock.com/faqinfo.html