What I've seen done often is putting more natives (to your area) toward the top (the ones that can survive your local climate), and as you go down further putting things that handle or like more water. It's all a trial/error thing.
Chicago Botanic Garden has a ton of these -- the one in your pictures is from the CBG.
http://www.google.com/images?hl=en&s...=1920&bih=1007
In chicago they plant a lot of Cedum and native/hardy stuff that would normally go on a "Green Roof" -- maybe check out plants for a "green roof" for ideas. You'll want stuff that stays more in a clump, or is a vine. Also stay away from anything considered an invasive species in your area...you'll have that shit growing all over your entire house in a few weeks!