Hi, Anders. I can't tell you directly, and the idea of sawing and splitting enough to do even a small roof gives me a migraine, but someone who does know is Roy Underhill, the host of "The Woodwright Shop" show on PBS. His books are listed at http://helios.oit.unc.edu/uncpress/woodwright/
I didn't wander around that site looking for an e-mail address for Mr. Underhill but I'll bet you can find one on that site or thru the University of North Carolina. I'm sure that you use a froh and mallet but I'm not sure how you orient the wood when splitting. Also, I'm not sure if you split freshly downed wood or after it has dried easier. I think that freshly downed wood splits easier though.