What flat roof material is the least toxic?

We’re getting thermal solar hot water. And the roof turns out to be not up to code on that part. Replacing it is expensive, but it looks like it has to be done


They recommended rolled roofing, but that is definitely petroleum product, and I don’t want water coming off of that going into our garden. Then there’s metal roofing, and there are several different kinds of that, and my assumption was aluminum is the least bad, but the contractor said it has to be steel. I’ve heard bad things about galvanized steel, not to mention that it really seems to break down pretty fast.

It doesn’t look like a living roof is in any way an option here, especially since it’s going to be under a solar panel, what suggestions or information do you have? Thanks.

bumping this -- any help would be most appreciated.  I trust no one haha.