[Cob] The best roofing?

[Rodger Chenoweth]

Greetings everyone,
I'm new to this world of sustainable building, and new to the love I  
have for it.
In my mind's natural building wanderings, I'm always up against the  
ROOF.  Foundations seem like they've been tried and tried again until  
tried true... but I haven't come across a cheap, natural roof that  
feels trustworthy.  I feel hesitant to put just a thin layer of  
plastic in a living roof between me and the elements... although a  
living roof seems the best.  One hole... and it's all over.
Could you share with me your preferred roofing ideas?  And comment on  
living roof proofing?
Many thanks, I look forward to your ideas,
Cheers
Rodger