Is an open top run ok? or should I stick with a fully enclosed run?

[CoyoteMagic]

I had a run without a top for 3 years. If you close your birds up at night, you won't have to worry about owls. I've got hawks nesting in the woods all around me. Never lost a bird to a hawk, owl, etc..... You need to provide cover for them to get under in case they spot one. Chickens, especially roos are very vigilant about what is going on around them and will sound an alarm. Guineas are even better (?) at sounding the alarm. My husband refers to them as Air Raid Sirens!