When installing a French drain, if using the white PVC with holes drilled into the pipe, the holes go facing down not up. Otherwise the ditch needs to be nearly full of water to start carrying the water away. With them pointing down the water level only has to come up about a half inch for it to start flowing down the pipe. I'd recommend the PVC versus the corrugated black plastic as it is easier to keep free of silt.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.