Here are the specifications for the ADA recommendations for maximum rise of a wheel chair ramp.(People who don't use a wheel chair can still walk up these ramps without problem.)
ransomnote: Now compare that angle to the roof in the image Steven W. posted:
That roof might be 1 in 12. Contrast my house with is more on the order of 5 or 6 in 12. Steep. Although the guy from Allstate, while denying my roof claim, climbed right up on there. Carefully, of course.
Oh my ... Speechless