If you only have one roof, do you go for the green one, the rainwater harvesting one or the solar panelled one? An eco-savvy friend of mine insisted you could do all three at once — you can work it so that the green roof also channels rainwater down into a reserve, and solar panels can go along the sides, or they don’t even have to be on the roof to begin with. Perhaps you could even throw up some wind turbines while you’re at it. But maybe it comes down to cost, or practicality, or maybe a peaked roof is more conducive to certain options than a flat one, and vice versa. Anyone got an opinion on which roof wins the green prize?