To be honest fly screens are pretty cheap to get made and it's hardly worth making them yourself, I used to make them and fit them as a job when I was about 17 or 18, and when we build our house recently I got a quote, and decided it's not even worth doing yourself (and I still have the tools and some materials in my shed) and I paid someone to do them and fit them for me, I even got the pet proof and fire/ember proof ones as I am in a bush fire region and the price was pretty cheap.
There is a bit of a knack to making them as well, if you have not done it before you will stuff a few before you get one rights as the frames are flimsy and deform easily when fitting the actual mesh.
And I am the sort of person that will do most things himself, I just completed about 300 meters of fencing as I could not justify paying someone to do it.