I have a small maple in the middle of mine, and I couldn't determine how to roof it with the tree there either. Not a huge deal until the hawks found my yard. I read on a post (which I can't find now!) that someone used fishing line as a deterrent. It was mid-winter when the hawks set up camp outside my yard - so I wasn't going to be building anything anytime soon. I figured I might as well try the fishing line, or it wouldn't be long until I lost another of my sweet little Bantams!
I bought the heaviest gauge, cheap, clear line I could find. Then I strung it from point to point - all over the crazy place. The more haphazard, the better. I started in one spot and just kept wrapping around posts and the tree, pulling fairly taught as I went. When I was done, I tied off the end. It ends up looking like a spider web, and the hawks have a hard time pinpointing it, apparently. I kept it higher near the entrance to the coop and the gate. If I bend over, I can walk under the rest, but that was the only way I could manage it in my particular yard. I do have to say that sometimes I forget, and I clothesline myself...then I laugh. I think the chickens laugh, too, actually.
Anyways, it is now June, and I haven't lost another Bantam. Sooo thankful for that!!! I actually had a hawk fly down as I entered the yard one day in December/January. All of my chickens had run over to see me, so there guard was completely down. It flew down within 10 feet of me, talons first, but it hit the fishing line, just about bounced off, and flew to a nearby tree. That was just enough time for all of the little ones to make it through the chicken door to safety, and the larger flock leaders to get set for battle. (I don't have any roos.) So I saw the line put to the test, and it (at least once) did its job.
Hope somebody finds this helpful...and MANY, MANY thanks to whoever it was that suggested the idea in the first place. If I could find you, I would give you 100% of the credit for the idea and for saving my girls!!!
-Cyndi