I made a couple of bug nets for my wide brim hat. Considerations: size of holes. All the commercially sold bug nets I could find in 2018 (US, UK) either had holes that were too large or they were too small and laid against my skin so the mosquito can zap you right through them.
I decided on making them so they completely ‘bag’ my hat, brim, head and shoulders, held in place with the under arm bungee loops. They work great. Not hard to figure out. The best approach is make it bigger than you think you need and then sew tighter seams to scale it down. (If you’re a sewing machine noob as I seem to remain, when you think to add 1″ for a 1/2″ seam, add two inches) Sewing the noseeum mesh is a bit of a pain, looks ratty – but works. You get better with practice.
The mesh I used was the lightest weight smallest hole stuff sold on RipStopBytheRoll. (The way I measured holes/square inch was to make a 1″ 10 x10 grid in Illustrator print it out on a laser printer, lay the fabric over it and count the holes in one 0.10″ square. I think I got >60; so >600holes/sq inch.  Hope this helps.