They sell full kits on BRS but I went to Home Depot and got 8' sections of window screen framing for almost nothing. Then you buy the corner pieces and the rubber spline and boom, you build a screen window
Glass is actually quite bad if you're talking about covering all or much of the top of the tank. Clear mesh will not block light and does not prevent the gas exchange from occurring. Him using the 3-4" piece in the front won't hurt but I would stay away from using the middle piece as well.
Sure, with a completely open top you're going to lose water faster due to evaporation. However, this is actually a good thing in my opinion because it's like a "hands free" constant water change which can help keep nitrates down.
I'm no seasoned pro but I would use the clear mesh that BRS sells. If you want to come check out the top I made for my frag tank last night shoot me a text. Once I make the one for my display I might have some left over for you.
Oh, and I guess you're stuck using the glass in the front.
Frag tank is plumbed, filled, and up and running. I added a decent sized piece of flat shelf rock in the tank and about 15 pounds of rock into the sump that I had lying around, along with a few pieces that I grabbed from Richard at ERC. I gave the rock a nice acid bath and rinsed it off real well then soaked in some RODI for a bit. I had a HOB filter running on my display the past few months which I was running GFO/Carbon in so I switched that over to the frag tank to seed the rock. Ordered an AquaticLife 115 skimmer last night and a new heater which should be in by the end of the week. Also should be getting my new d120 in a couple weeks. By the time the light comes in, the tank should be stable and ready to be stocked!