I found some basic instructions and images at Natural Life Network
Here they are:
Simple Design Overview
The basic design and construction of a green roof can be quite simple and inexpensive. Given the additional loads that a green roof requires engineering will be required to ensure the correct level of support structure. The basic design of a green roof is as follows:
- Plywood layer on top of roof trusses or joists (some slope is required for drainage, too much slope may be difficult to cultivate due to erosion).
- Apply a synthetic rubber membrane on top of the plywood roofing structure. Up to this point you have basically created a common industrial roof.
In order to retain the soil the roof must provide a containing edge from four to eight inches high, also covered by synthetic rubber. Don't forget to leave some drainage scuppers.
- Once the base roof water proofing system is in place the additional green roof components can be added when ready.
- The first layer of the green roof is typically a foundation membrane (a dimpled "Delta" membrane or something similar that can catch and retain some water in the little cups.
- Add a landscaping root barrier membrane. Apply the all membranes from bottom to top and ensure layers overlap with upper (higher) layers on top of lower layers. (The same way you shingle a house).
- Around the drainage zones create a drainage area as you would around the foundations of a house, with gravel and drainage tubing.
- Fill in with soil from four to six inches.
- Use straw mats tucked under the soil to reduce erosion as the soil begins to grow plants in it.
Check out www.GreenRoofs.com