The typical french drain can put more water into the ground than is diverted from the area. Water has to pool in the gravel up to the flow line before the pipe even starts removing water. If you use them, make sure the base of the trench and the pipe have a 2% grade. Downspouts should discharge into solid pipe, or onto grade sloping at least 2% away from the structure. Perforated pipe is an invitation for roots to grow into and clog the pipe. - install cleanouts if you use them. If you drop grade through the entire area and slope it away from the house french drains should not be needed. If you use an impermeable surface (concrete, plastic sheeting under pavers, etc.) you can use a flatter grade - as long as it slopes enough to drain.