What factor is crucial in determining the slope of a roofing system?

The expected snow load and weather conditions are crucial factors in determining the slope of a roofing system. A roof's slope directly influences its ability to shed water and withstand various weather conditions, including the accumulation of snow or rain.

A steeper slope may be beneficial in areas with heavy snow loads since it helps prevent the accumulation of snow that can lead to increased weight on the structure and potential damage. In contrast, flatter roofs can collect water and become prone to leaks and structural issues if drainage is not adequately managed, which is particularly important in regions with heavy rainfall.

Understanding local weather patterns, including average snow loads and rainfall, allows for proper design that both supports the roof's functionality and ensures structural integrity across varying environmental conditions. This is why option B is the correct choice, as it highlights a critical consideration in roof design that directly impacts performance and longevity.