I contemplated shingling my own roof three years ago. It is a 2 storey house with a 12 on 12 pitch. From peak to ground, the distance is around 32 feet. I had roofers come in and do the whole thing (over 1400 sq feet for just 350.00 CDN) Don't laugh but that that is what they quoted and I jumped at it - who wouldn't? And it is a class A job to boot.
Just a day before they started, I decided that something needed to be touched up before shingling could start. To make a long story short, I fell from the ladder (about 14 feet from the ground) landed neck-first on the compacted gravel and fractured two vertebrae in my neck, shifted two of them out of line and fractured the heck out of my right elbow. I only spent a few days in hospital but four months in a special neck brace (metal bars, straps and other restraints). My elbow is still screwed up - no full extension. Neck just gets a bit stiff on times.
I built the entire house myself without any other mishap. I even did the clapboard/windows while in the brace - stupid, yes but it had to be done before the winter came
Moral of the story: When it comes to something as dangerous as roofing and you have to ask very rudimentary questions regarding procedure - DON'T DO IT!
P.S. I have since been to the peak of my house to clean the chimney (I have a wooden ladder permanently laying on the roof and a small platform bolted to the end of the ladder) but I now wear a safety harness.