UV-resistant plastic that does not degrade with repeated temperature cycling costs more than shingles at the moment is the way I understand it.

There are premium roofing shingles and tiles made from plastic. If you see an unusual color of slate roof with regular shaped tiles or a repeating pattern of a couple feet, you may be looking at one.

Cost wise, they fall between asphalt shingles and clay tiles or slate (that's a big spread). They can last better than asphalt and should need fewer repairs if you live in a hail or extreme wind area.

Here is a project that got plastic slate recently. http://www.professionalroofing.net/webexclusives/webexclusiv... The extreme labor cost and difficulty of access to repair justified the extra material cost.

Slate roofs are made from slate, not plastic.

But people don't always see what's really there

Shingles are made of asphalt, derived from the lowest grade of oil. It's so cheap we paint it all over our roads, too.

Not only is it made from the lowest-grade oil, but this low grade oil constitutes the majority of all the oil (and near-oil substances) that's left, e.g. tar sands, oil shale.