Not sure mine is Aqueon, but the measurements are 4" to front edge of hinge, the piece of glass is 4.5" total (.5" sticks inside of hinge). The entire unit is 2 pieces of glass each 4.5" and an inch for the hinge, making it 10" in total. Hope this helps.
Above are the glass lids I have on my 75g. The glass in front sits on the inner lip of the tank, and slides back, no hinges. The glass in back just sits on the top of the tank. I was leary at first, but after seeing someone's fish room, I went for it. They do not slide off.
I got the glass cut for me to my exact measurements. It saved me maybe 10$ on all 4 pieces, so not a great savings, but I will do this again next time I have a glass lid break.
I don't have to add any water to my 75g between weekly wc's, and I have a 3bulb T5 fixture over it.
I forgot to add I have those plastic strips attached to the back glass, which aids in the back glass (which is sitting on top of the tank) not sliding off the top of the tank. If you look closely you can see them in the pic.
I might try it your way, I'm just trying to limit the evap. as much as possible because I'm gonna have a lot of water in the room when its done. The room will be pretty well insulated and sealed off with a dehumidifier and possibly an air exchanger, but the houses in my area seem to be at risk for mold, which I won't have.
The first stage will include the tanks I already have (55g,40b,20h,2.5g fry tank) plus the first rack that will hold nine 20 longs. I built the rack for my 40 breeder to also hold three 20h, so I will also get two more 20h to fill that up.
Once that is all up and running, there are plans to add some bigger tanks (maybe two 75g and a 125, and possibly a 4'x8' 318g)
Right now I am re-routing and upgrading electrical, and some other household utility type stuff, but when the real fun starts I will be sure to take plenty of pics for everyone.
I'm not sure about full auto water changes, but it will at least be set up for easy water changes. I'll probably have 1 or 2 55g plastic barrels for tank temp de-chlored water, with a submersible pump to fill tanks, and a powerhead with a hose to drain tanks to basement sump pump.
I'll do some research on the auto setup, but I'm trying to avoid 6 miles of pvc piping. The tanks will be powered by air, not a central water system. If I was doing a central water system with a sump, the auto W/C would be a no brainer.
edit: The rack of nine 20l's will be air, I will use my existing power filters for 55,40,20h's