McKinney covers a wide mix of housing. The neighborhoods around the historic downtown square have older homes with mature tree canopy, where open gutters fill steadily through the year and fascia boards have had decades of exposure. Newer construction west toward Custer Road and north along Highway 380 brings larger rooflines, steeper pitches, and bigger volumes of water arriving at fewer downspouts.
Both call for the same thing, just in different proportions: enough capacity in the trough, enough downspouts for the roof area, and discharge far enough from the slab to matter. North Texas storms tend to deliver a lot of rain in a short window, and a system that keeps up with a gentle shower can be overwhelmed within minutes of a real downpour.