I was once in your position. I had just built a small coop 4' x 4' for two hens, and I wanted a small enclosed run, and I wanted to get it built fast. Pause here to stress the fact that the biggest mistake I have made building coops and runs have been thinking too small.
I was given heavy steel hog panels and it was easy to put them up. I used the same steel panels over the top of the sides to support plastic sheeting for the roof. You probably don't need to be concerned with snow load, but I should have taken snow and wind factors into consideration.You do have rain, however, and rain water can quickly do what snow does to plastic sheeting, puddling and then caving in. Wind one day tore the sheeting off the run roof and nearly gave my chickens heart attacks. Trying to control madly flapping plastic in a 50mph wind storm was a nightmare.
I tell this story to give you the idea that it pays to think carefully before you build a run. Consider all the weather extremes you may face because you will experience them sooner or later. Build strong. They may be just five pound chickens but a run that isn't strong could collapse on them and kill some.
Eventually, I budgeted for a new run and had it framed with strong lumber. I bought fiberglass panels to roof the run. They were easy to install, however, last summer, a severe hail storm punched golf ball size holes in the roof. I bet you get that kind of hail. One hail stone came through the roof and narrowly missed me and the chicken standing at my feet. It would have knocked me out and killed the chicken if it had hit either of us.
Think big. Think strong. Resist thinking cheap.
