Understanding the numbers
Roof pitch is the rise of the roof over the run of the roof. The rise is the height of the roof, from the base to the top. For example, if a roof is 8 feet high and spreads out from the center covering 12 feet in each direction, the rise over the run would be 8/12.
Consider a right triangle. The bottom, horizontal line of the triangle is the base of the roof. The straight, vertical line runs from the base to the top for total height. This distance is the rise. The angled line, from the top to the base, is the slope or run of the roof.
Roofing work is dangerous, and the more a roof slopes, the more dangerous it is to work on. A roof with a pitch of 3/12 to 6/12 can be walked on without difficulty. When the pitch reaches above 6/12, the slope becomes difficult to work on.