For my 8" i3 I have glass that is 8-3/8 x 8-3/8. I scored and snipped off the corners just a tiny bit to miss the bolts on the bed. I then used an orbital sander with 120 sandpaper to sand all the edges nice and smooth so when you handle and wash you don't get cuts. I have 3 sheets and just keep cycling them. I went to the local hardware store and just got inexpensive window glass. I looked into the fancier Pyrex/equivalent that people said was best due to thermal expansion but each piece was going to cost $90. I've had no trouble at all with window glass at $3.25 each.

Can't wait to see photos... I want to do the upgrade when it's available.