Final answer:
The question deals with engineering, specifically the sizing of a drain leader for a roofing system. The answer would require reference to local building codes and consideration of rainfall rates and roof area, but not enough information is provided to give a precise size in this instance.
Step-by-step explanation:
The subject question pertains to the field of engineering, specifically to plumbing systems and their design. The minimum size of a drain leader is typically derived from local building codes, which provide guidelines based on the projected roof area and the local rainfall intensity or rate. Although the question does not give enough information for a precise answer, as one would need plumbing code charts or calculations that relate the rainfall rate and the roof area to the diameter of the drain leader, it generally involves calculations from the International Plumbing Code (IPC) or equivalent local codes that consider factors such as the maximum rainfall intensity, the drainage area, and the type of drain.
To determine the specific size, engineers would refer to tables that consider the aforementioned parameters, ensuring proper drainage and preventing potential water damage or flooding. Rainfall rates and measurements, such as the ones mentioned in the sample data from Table 1.16, inform these design decisions.