The slope of the roof horsetail shelf and the roof slope must be the same?

The slope of the roof rack to the original old-fashioned algorithm is, 5 minutes of water, 5 minutes and a half of water, 6 minutes of water, the rural areas are generally covered with tiles, are 5 minutes or 5 minutes and a half of water according to the calculation of the water, I'll tell you the algorithm to 5 minutes of water calculation, that is, 1 inch down 5 minutes, you are a 15-meter span on the 15 / 2 = 7.5 / 2 = 3.75 meters.

Slope calculated by a factor of 1.11, is 7.5 * 1.11 = 8.325 meters This is the old algorithm before.