Here's some options in and outside of your question. With the assumption that you're referring to the wood ( Plywood ) decking itself.
- Look for FSC Plywood, which is sustainably harvested.
- The membrane, itself is the water barrier. Require 2 layers of the membrane.
- Use the lightest roof possible. White tile, white elastomeric if it's a flat roof.
- Consider using a ceramic coating over the membrane, under the roof covering. ( Tile, shingle, etc. ) Look for SuperTherm. spicoatings.com
- If it's flat, consider a vegetative roof.
- This is the most important; Close off the attic space. No soffit vents, no roof vents, ...no vents at all. Apply spray foam insulation to the underside of the decking. Bring conditioned air into the attic from your air handler, to condition attic air. ( Not cool/heat ) Just condition. The attic will then become part of the conditioned envelope which will increase the home's energy efficiency by as much as 50%, eliminate moisture, insect and mold infiltration.
- Finally consider a cement roof. ie. www.wrcscorp.com or http://www.insul-deck.org/ Yes, more expensive. But good for 100 years, energy efficient, super strong adding durability and strength to the whole home.