Imagine if I asked a builder to build me a yurt. Or, maybe a traditional Japanese home with wagoya construction methods, a genkan, or washitsu. You might imagine his/her response may be something like "I'll need to research the topic, methods, requirements, and processes, then discuss it with my tradesmen, then prepare a proposal for you." If they take on the project, that means new skills to learn and to teach their tradesmen; new permit requirements; new architectural, design and engineering details; new suppliers to work with; new products to price out; and new timeframes to learn. That all takes time to research, to learn, to process, and to implement. Time is money. Plus, (s)he doesn't necessarily have the personal experience to know how the finished product will work out--will everything work as expected? Will they know how to service and maintain the facility? Do they need to build in extra costs to the proposal as insurance for the unknown--to cover additional time and replacements?
"Building green" is exactly the same thing to a builder that doesn't have experience with its specifics.
Of course, it may be more straight forward to hire a team--builder, architect/designer, materials supplier--that can talk the talk and walk the walk of building green. Experience carries great value and can substantially reduce confusion, delays, mystery, and extraneous costs. And regardless of what you are building, a team that prioritizes good communications and process is more bound to succeed.
If you do choose a team that doesn't yet have (much) experience with the methods and materials you'd like to use, it's helpful to be sympathetic to their concerns and questions. Ironically, it may seem like you need to help them with your project as much as the reverse. Keep this in mind when thinking about your project and goals, and who will help you get it done.