I made some custom glass tops for my 90 gallon, since I didn't like the hokey plastic back strips that the Aqueon (All-Glass) tops have in the rear.
Glass tops that size are 3/16" thick. That's thicker than window glass, and thicker than what's carried by home centers like Lowes or HD.
I wouldn't use window glass - too fragile and unsafe, and you're asking for disaster.
Go to a glass shop and they'll do whatever you want. I just got two rectangles of 3/16" glass, and drilled holes and notches myself, but they'll do that, too, if you want them to.