I have been using glass for about a year now and never had any problems, I just used the glass out of a picture frame cost me £1 then I use PVA and water mix 2 parts glue to 1 part water and paint it on with a small brush, then place under a low heat grill this dries the glue but also makes it even out fine
I just lay the glass on top of the bed and use bulldog clips to hold in place.
So far I have used PLA, Bendlay and Nylon with out any issues. I have the parts for the hot bed just not got round to putting it all together and with the glass way working so well not in a rush to just yet.