General contractors often do not have any control over what they build, or where they built it. They can use their influence to encourage projects to pursue 3rd party sustainability certifications like LEED, Envision, SITES, and so on, but ultimately the final decision on this comes from the project owner. The one thing General Contractors do have control over (usually) is the practices that happen on the construction site. Green Badger has created an extensive group of resources to help general contractors with improving sustainability on construction sites.