How to divide water when building houses in rural areas

What do you mean by dividing water or how to calculate it? If so, how to calculate it: dividing water is the slope of the roof! The algorithm for dividing water is to multiply the half depth (that is, the width) of your house by 4% (for example, the width of 6M is 3M times 4%, which means the height of 1.2m). Inclined from the horizontal position of the front eaves and the rear eaves to the middle ridge)