Hi all, this is my first post on this forum. I'm still making my plans for my chicken coop before I start gathering materials. I would like to have a garden on the roof, above the chicken run. I'm searching for different ideas to protect the roof from being exposed to water...for fear of it then not being able to hold the garden. A type of plastic possibly to put on the roof between the wood and soil substrate? Any info would be appreciated! Thanks in advance.