Ditto the above re:engineers. I know it sounds expensive, but its a lot cheaper than buiding a barn, watching it fall over, cleaning it up, and building another barn to replace it. And you may be surprised that it is cheaper than you think to hire the right people.
Do go to your town's engineering department and ask to talk to a planner as well as an engineer before you begin too much stuff. You may be surprised by some of the suggestions you get, adn some of your site requirements.