vertical garden and green roof what next

I have just undertaken a new project with some of the specification being a roof garden and a vertical garden to the frontage of the property.The idea of the living roof or greenroof is to insulate the property and help control the storm water run-off. In this case a light-weight medium has to be used due to the structural conditions of the property . Expanded clay/ volcanic rock will be the medium for the roof garden as it's light and will be ideal for cacti succulents and aloes which shall be the mainstay of the roof.