An alternative drain system, one I just had installed BTW, uses perforated 6" flexible PVC hose with a sock over it installed directly in the dug trench with no stone. It works even in the heavy clay soils where I live. It is much easier to install for a DIY project; you could put stone on top if you want it for aesthetic reasons, but it's not needed. It is pitched at 1/4" per foot.

I'm betting your son will be asking for something besides the skateboard before the trench gets finished.

John