The answer to your question could fill a book!!!
I suggest you go to the BYC forum and look down to coop design. Click on that and read for hours!!!
I learned the hard way, that chicken wire does not protect chickens very well...... in my early years I used it on the sides of the pens and soon learned neighbor's dogs or whatever can chew through it without much effort!!! Go with hardware cloth added to something stronger...........but it all really depends on where you live and what kind of threats you have.
Hawks....I've started using fruit tree netting to cover my yards. I've seen other folks talk about using baseball netting to cover their yards...
Best of luck,...since EVERYTHING loves chicken, we have to figure out how to protect them from EVERYTHING. But because we love them and their eggs we are willing to work to figure out how to do it. I keep refining my coop/yard.....every year I learn something new.
Cost, looks and longevity of the product can be considered. Maybe good galvanized after weld will suffice. If you want a different look then vinyl coated gaw weld is another option. It can be costly to buy higher end wire but it will last longer. Then again the less expensive stuff may do the trick for ya too. I would read the posts suggested and figure out what your priorities are. Other than chicken safety, is it the cost or is it the longevity of the product or is it the cosmetic appearance of it or a combination of these that you want to achieve?