Once they experience freedom they are hard to keep in. I have a 72 inch fence that keeps them in. I made the mistake of putting some hay bales around the coop for the winter to help keep the winds off. They were 72" high but the chickens figured out they were flat on top. They were all out is short order. So we clipped their wings on one side only. Eventually they forgot they could fly and we haven't had to clip their wings again.
My run is 6' tall, but I also have bird netting stretched over the top of it to keep the chickens in and the hawks out. It comes in 20' lengths and is pretty cheap at the feed store, but if your run is huge it probably still won't be practical. I would guess wing-clipping would be a good way to control them. I used to have a Parakeet and we clipped a few of his wing feathers.
You might try stringing twine across the top, in paralell about 4" apart. Maybe with streamers hanging from the twine. The chickens couldn't spread their wings through it, and it would deter hawks. Maybe even a aluminum pie plate or two (small table talk type of pies) for flash and further hawk deterence. Might also keep regular birds out of your chicken feed, which ain't cheep! hehe
I put a top in mine too. I left it short but made the top of light removable panels that I can easily lift back off for cleaning, or if I just need to get in there. That way I do not have to get on my knees.
I have a bit of a dilemma quickly approaching. I have 17 chickens that are free range. They have a v-e-r-y sad coop with a 4' high run partially covered with a tarp. Their food and water are in there. No, we're not that ghetto, but as soon as we bought the supplies to build their awesome coop, the guy who we were leasing-to-own the house from decided to sell it out from underneath us.
So, we close on our new house a week from tomorrow. There is a coop there, but I don't feel comfortable letting the chickens gallivant free in a brand new place. The oldest are around 16-18 weeks and can fly right over a 4' fence. The new coop is 8'x8' or 10'x10'. What size run (temporary for about two weeks for the 17 chickens, will eventually hold 6-10) would be appropriate? Should I clip a wing? Use poultry netting? Any help would be super. Thanks!