For the girlfriend's trailer.





It is older ( mid 80s )   with a flat roof,  it has quite a few sags and low spots in it.    A couple years ago the wind storm did some damage to it,  and basically tossed a few rolls of asphalt over the old one,  and it held fine.     But this inter has been pretty bad and there is some significant ice on it,   which actually pulled away part of the roof from the top of the wall.   SO the back bedroom is getting water again.    (of course we just finished doing the inside )     When we redid the inside,  I noticed allot of cracked trusses, so I basically attached 2x6 to them all and then supported those by building new walls and insulating everything better.   Came out pretty good.    The Small rooms I did not do anything with the trusses.
SO   I am trying to come up with the best and least expensive way to help her out.        It is a 12x60'  the middle 30' is about 6" higher than the two ends. (front to back ).      





While I may not be a roofer,  I do have a little bit of understanding and have done a little bit of both flat and pitched roofs.    





What I am trying to figure out is which would be the least expensive way to go with this.    I have not really started pricing anything,  hopefully someone in the know could direct me.  
Plan A


Rip up existing asphault, and go over it with the ply board (  Need help here,  not sure of the name.    foam board with tar paper on 1 side),    and use the GAF liberty low slope system.  http://www.gaf.com/Roofing/Residential/Products/Low_Slope_Membrane/Liberty
Plan B





 Rip up everything,  screw down OSP,  and go with GAF Liberty roll membrane system Or at least prime the OSB and put down the BASE/Ply sheet and the CAP sheet.
Plan C  





Build a perimeter around and make it all the same
height, the put trusses in with a small peaked  roof?   I would probably
need 31 of those plus the OSB to go on top.   then regular asphalt
shingles.  
I can use a sheet metal brake to make aluminum flashing around the parameter.   ( albeit only 3' sections )
 

you sure on that age? though flat roof stopped before the 1980s.

Trusses and metal would be the best long term solution, but realistically how long does she plan on keeping it?

Title says 82    
Realistically, probably another 10 or so years.  
Trusses and metal and build like a pole barn by laying 2x4 long ways across the trusses and screwing the metal to those?
 

around here I have seen a bunch where they just put up 4x4 posts and build a whole new roof over em

I would do this, you could turn it into a pole barn later if you don't need it for a trailer.