The large-area facilities are mostly based on the same materials and construction technologies. However, the larger the roof area, the more difficult it is to ensure the proper functioning of the emergency roof drainage system, which is most often implemented by means of emergency roof overflows. The problem is confirmed by at least several construction disasters caused by sudden and intense rainfall that have occurred in the last 5 years. The paper refers to the method of calculating the design rainfall intensity, as well as the definition of emergency roof drainage available in the literature. The effect of deflection of the structure from individual load cases, including standard loads, as well as from rainwater load in several variants, depending on the assumed snow load zone, is presented on the basis of a sample structure. The calculations show that structures with variable spans are particularly susceptible to the accumulation of rainwater. Due to the complexity of the phenomenon, the author does not provide a clear solution to the problem, but recommends the use of a double pipe emergency roof drainage system in such structures, rather than relying solely on roof overflows.