What I have found that has worked best for me is to ask the realtor for a referral of a good handyman, contractor, roofer etc. once you find one good worker that is vetted and verified by someone who is in the industry you can work through them for more referrals (plumbers, electrician drywall etc).You will need to make a few trips down to check on the progress and meet the workers but that is part of the fun in the journey. 

Lest you begin to think I am lowballing, I have paid what each contractor and roofer has asked for in cash, without hesitation.  

As an investor I have a variety of human resources at my disposal: carpenters, plumbers, roofers, realtors, etc.As an investor who's been around the block I have actual experience in each of those areas.

Had a roofer fall off one of my roofs.

Roofers will cover the existing plywood instead of replacing sections when there's enough damage.

In other words a GC might charge me 8k to do a roof, when I could hire an experienced roofer who will do it for $4,500 and all I have to do is pay the WC on the salary I pay him.

For example, roofers in one area can charge vastly different rates than roofers in another, mostly due to local ordinances regarding permitting, licensing, insurance, minimum wage laws, etc.  

Bert bet would be to get a roofer to check it out and pay them to write you a letter you can include in your listing explaining the life remaining. 

My GC had a roofer but has been unresponsive so looking for options.Thanks

I've needed people from electricians to roofers, foundation experts and mainly just a very good general handyman.