Long-span structures are more vulnerable to the imbalanced distribution of snow loads, which is a primary factor contributing to structural failure. The development of snowdrifts is directly related to the shape of buildings, as it significantly affects turbulent characteristics and the process of snow drifting. This study explores the evolution of snowdrifts on a long-span saddle-shaped roof under various wind conditions. The numerical k-kl-ω model is validated against observation data by testing the flow field and snow distribution features of a stepped flat roof and a wind tunnel test. The snowdrift on a long-span saddle-shaped roof is simulated using the proven method, and the snowdrift's properties are studied at different wind speeds, wind angles, and threshold friction speeds. A comparative analysis of wind-induced snowdrift development on open and closed roofs is given, and the snow shape coefficients for each roof partition of the prototype roof are also provided. The findings indicate that the characteristics of snowdrifts on the roof vary with changing wind environmental factors, and the adverse inflow velocity and wind angle are identified. Snow morphology variation is more subject to an influence on changing inflow velocities compared to an alternation in wind-blowing time. The study reveals differences in how wind-driven fresh snow and long-deposited snow distribute themselves, with fresh snow producing more unevenness, potentially affecting roofs' load-bearing capacity.