Mike,
Although I am retired now, I used to work in the oilfield and can imagine what you are going through. My radiation/chemo treatments wiped me out Can you get a desk job with your compsany, or a roofing company supplier? As a professional roofer, you certainly know the business and would be a tremendous asset with respect to bidding and scheduling jobs.
I don't know if that is realistic, but it can't hurt for you to look into it. You've got to fight.
Best of luck,
Peter