I had the same issue but different. Herons stealing the coy out of my fishpond. All i did was build a mesh fence around it. They make the mesh in flouresent orange or black,(better landscape stores should have it or look on line. All you would need is some posts to attach it to I used ( 4x4s), and "cap" the chickens area with it. Just make sure you get a mesh thats small enough to not allow the hawk to get tangled up in.(dont want to hurt the bird) The mesh is dirt cheap,and if you can use a post hole digger and a staple gun,your set. If you have a larger area,its available in some pretty wide widths, or overlap the seams and zip tie them together.(you might need an extra support or two depending onthe size of the area.
I wouldnt think that you would need it on the sides, just the top. Depending on the size of your area,you should be able to do it for about $100 +/-
Worked wonders for my fish pond. And after a month or so, the herons figured out that the free meal was gone,and i was able to break it down easy and put it in the poll barn for future use