Vegetation on top of a wofati house?

I been interested in wofati for a while...I am still trying to decide on what kind of house I want......anyway based on my observations it seems that most people choose to use grass as the primary vegetation that covers the roof....is it possible to use blueberries or blackberries instead....I think grass is just a waste when I could be using that space growing food instead....I think perennial crops would be bests to limit erosion. thoughts?

I've heard of folks growing squash on their roof, though I can't remember where I heard that.

Something that's relatively shallow-rooted seems like a good idea, I'd be afraid of deep taproots punching through the membrane.