Are you thinking of covering an outdoor Lunch/seating area?
Tension Structures and Shade Sails are the perfect alternative to solid roof structures. They can be used to cover large outdoor school or commercial areas to small backyard alfresco area.
A cantilever is a very modern solution especially when you require less posts in an area or you do not want to obstruct a view.
A Barrel vault is perfect when large areas need to covered with long spans. Other alternatives are umbrellas and framed structures.