How much suitable slope of sloping roof, how much suitable slope of sloping roof knowledge

First of all, I personally recommend that the slope of the villa roof using 15 ~ 30 degrees is the most appropriate, when the slope of the pitched roof more than 30 degrees, it is not easy for people to stand or walk on top of the pitched roof, which will give the construction of the personnel or later maintenance to increase the difficulty, but also exists a certain degree of safety hazards. If the slope of the sloping house is less than 15 degrees, it may cause poor drainage or water leakage.