adhesiveglass
I am searching for strong glue that
I already searched that some blends of silicone and polyurethane adhesives are used to bond those two together, but I don't know about the cold weather resistance.
The T-square is just that - a T-square for making sure that the glass is cut square, unless it has an integral glass cutter of course.
The tool they use is a glass cutter. It will have a diamond wheel or tip and scores the glass where it needs to be cut. Then a sharp tap will (hopefully) produce a clean break.
They should be easy to pick up at any hardware store. You might have more difficulty getting hold of a large enough T-square, but for a cold-frame you don't necessarily have to be 100% accurate.
Glass can be quite expensive. It would be worth getting a quote for buying the glass you would need and then compare to the cost of the tools you need to buy and your time.
However if (as chris points out in his comment) the glass is tempered then you won't be able to cut it. It will simply shatter if you try.
Suction cups are used with success in this situation. Search for "glass table suction cups". The cups have a small cylindrical nub that sits in a hole you will have to drill for each cup. You should only need about four. With the suction cups, the table would be secure, would have some (minimal) give when struck, and would be easy to replace.
Best Answer
Readily available products will include clear epoxies and marine grade silicone adhesives
Auto/Marine silicone sealant is typically rated to -40F, up to 350F and is quite clear between 2 pieces of glass, I do not know how the solvent will react with the PC in terms of changing the clarity of the surface. It dries like a high durometer rubber and can assist in noise/vibration damping from one surface to the next. These take at least a day to cure.
30-minute epoxies harden solid, but have a lower temp range, around -60F to 180F. They get HOT when they cure, which can lead to warping of certain plastics, but when bonded to glass this should not be a problem.
Optically clear lens adhesives are based on epoxy or acrylate and have a slightly more narrow range of temperatures, usally -40 to 150F. They are solvent free and are thus cured rapidly using ultraviolet light or heating (or both together). The lack of solvent should mean no change in surface clarity of the PC.