I just did a french drain behind my house. The spot where the house was built was just bulldozed out of the top of the hill and so the back is pretty close to flat. All of the drain water from the downspouts just got fired back there - drained OK, but I put the drain in because I'm going to put in raised beds and irrigate like crazy.
Anyway, they're easy to do yourself - IF you have a tractor and backhoe! I do /forums/images/graemlins/grin.gif. But even just cleaning out the trench and then spreading the gravel is a lot of work so I would not want to do it myself if I had to dig it by hand.
But all you need to do is dig trench, put gravel and perforated pipe in (wrapping with landscape fabric is a good idea, and I did that in mine). Takes quite a bit of gravel - I was surprised at how much. But is easy with the tractor.