Here's a picture of the relief slates on an old building. Not quite the natural slate look but they do look a hell of a lot better on a single story roof than the plain tegral slate. [broken link removed] - warning 1MB for the detail
I've recently installed a reconstituted natural slate (Cambrian Slate) with the material coming from Capco roofing via Lafarge roofing. I'm delighted with my new roof, and in a year or so will look like a real natural slate. See below for details