I think that adding a green roof would present an opportunity for the center to add insulation on the center itself. The standard today is R-38 or greater on any roof. I'd bet that there's little to no insulation up there now. Either way, they could benefit from throwing some up there, or in the interior of the building. This would give the building a better energy expense ratio at the very least.

On top of that, a green roof can provide up to 25% savings in summer cooling. Not so much in the winter.