Hawks are a big problem in many places. Even small hawks like the red tailed hawk can be found in urban areas. Especially now that the weather is breaking and everything is hungry! We've had hawks fly down into the chickens run and walk right into the coop. Of course this never ends well for the chickens, especially the bantams.
Unfortunately not every coop has a run that I can put a roof on. We've started adding deer netting to the tops of these runs and it's really helped to deter the hawks.
I prefer to put a solid roof on the run to keep out both predators and bad weather. That's not always possible, so sometimes you need to trick the predators. Oh sure, a hawk could rip through that netting but chances are they won't even try.