I'm using Imperial Rust-No-More
made by wilson imperial...
found it at the local paint shop
the guy had por 15 and thats what I was after. but he asked me to try this said it was much better than por15 and so far I believe him.
its a one step deal that you put right on the rust, no prep needed other than getting rid if the worst flakes and such, i bought a quart for 18 bucks and a spray can for hard to reach areas for i think 10 bucks, goes a long way, i think a quart would be enough for your roof, leaves a grey primer that says can be top coated with anything....
