They managed it at the Eden project. Or, you could have a go at something similar to what I did with my shed roof strawberry field. As a strawberry plantation it was a complete failure, because the soil was simply too shallow for strawberries and the plants dried out too quickly, but lots of weeds grew and thrived there after I'd given up on it, so I guess low maintenance, drought hardy wildflowers and grasses would be fine.
Yay spring! hi all. I'm back and ready to pull my wellies on and get lost in the garden, wish me luck. And hope you all got your thinking caps on as will have lots and lots of Q's