They are pretty cheap to just buy, aren't they?
I made my tank lid out of 1/4" bird netting and a custom screen frame. Really cheap to make.
Main reason I did that way is:
1: doesn't mess up any gas exchange happening at the surface, as the glass will block air flow, and the air above the water will get depleted of oxygen.
2: I have some metal halides on my tank. Putting a glass lid on it would be like turning the entire thing into an oven. I didn't want to fight that kind of temperature increase in the tank.
If you decide you want to do it out of the 1/4" mesh I have, I can give you whatever you need. I had to buy 14' by 6' min when I bought it, so I have tons left over. The screen edging parts cost just a couple of bucks at lowes.