I have some nice wood and i will make the frame myself. My only question is if mosquito net is good or it blocks too much light? I have small fish, so i really cant have much bigger holes. I have glass on the top now, but edges are not covered and i already lost 2 fishes because of that.
Have you tried eggcrate plastic? You can find that in the hardware store. I think the holes are 1/2 inch. The fish would have to have a darn good aim to jump out of it, and it hardly blocks any light. Mosquito netting sounds a bit fine and would definitely lower you light and might cause shadowing.
Depending on the dimensions of your tank , buy 1 set of corner pices for screen frame, $1.98 and 2-3 lengths of frame. or get the $11 kit that includes everything you need. Then buy a mesh laundry bag at the Dollar store. Cut the bag at the seam, it will give you a 48 x 72 inch piece of 1/4 inch mesh screen. Enough screen to redo your top several times. You can easily cut it if you need any holes for equipment .