Roof replacement, talking either metal or rubber roof is one thing. To repair damage to wood underneath, a whole nother story. May have to to take some of the siding off to get to the top part of the walls to repair/attach the new wood . Just a guess, anywhere from $3000 to $5000 and that could be parts alone, and maybe be more. The rubber material would be $1000 or so, plus labor. Not knowing the extent of the wood damage, hard to even guess, but don't be overwhelmed by the price.
By the way, you got a good deal, so you say. Did the previous owner not have insurance? Or maybe the insurance company wanted to total the trailer due to cost, and now you have a salvage title. Makes no difference to me, just something you might want to check out.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT