It wouldn't be a roof exactly. Because you can angle the panels and have much better transmission of light to the panel from not having to have a bike-proof coating, you wouldn't be completely covering the path and you would get the same amount of power from a strip that is thinner than the path, angled and fairly high up, this would cost far less money as it is available off the shelf, so you have more cash to spend on making more of it. Also, if you integrate it with lamp posts for your support pillars, you are not increasing the amount of street clutter either.