I’ve seen a couple of weather stations mounted on rooftops before, for example the station in Eureka, CA was on the roof of the post office for many years. This station in downtown Oakland, CA is unique because not only is it in on a rooftop, in the middle of an urban setting, it’s also over grass. Only in California would you find a rooftop with grass growing on it.
The large concrete pad and pea gravel/tar roofing nearby likely creates some bias, but is more likely to be swamped by the surrounding urban heat island (UHI) which is downtown Oakland.
See the picture below, click it for an interactive view, then click again to activate the Java panning applet.
This is COOP station 04-6336, which fortunately, is not part of the climate observing program. Still I thought it interesting and unique enough to bring to your attention as an example of a UHI centric measurement site.