Wooden shakes are a sustainable roofing material because they can be made by hand using a froe and locally available wood. You can make shakes from many kinds of wood, but the best shakes come from old trees with tight growth rings. Install shakes over roofing felt, and fasten with galvanized roofing nails. Steep roofs of 5:12 pitch or more will reduce risk of leaks and wind damage.
Wooden shakes can be used on walls and roofs built of pallets. See Pallet Roofs
Here’s a good article by Mother Earth News magazine on making wooden shakes:
The Froe and You: How to Make Hand-Split Shakes