I installed 4 stainless through wall scuppers with 3" main drains and 3" overflow drains to mitigate heavy rain storms associated with North Carolina Coastal hurricane storm events. I've piped all drains with 3"sch 40 pvc collection piping and 4" lead coated copper downspouts. I provided ⅛" per foot of slope on the 1000 sf rooftop deck that has been waterproofed by installation of Line-x material on roof deck sheathing and 18" up parapet walls. As installed, the scuppers with pvc piping and 4" diameter downspouts will drain 950 cubic feet of water per minute, the equivalent of 8" of rain in an hour. Call it overkill or over engineering, but that's what I wanted, to make sure my flat roof top deck would not become a problem over the next 30 to 50 years. Thanks, Copperlab, for making a product that, properly utilized, will provide many years of service. I'll keep in touch over the years and let you know how everything is performing.
Rick House PE