Hi there,
Now this might seem a bit "doom & gloom" but honestly it's not intended as such and there's a healthy dose of guesswork behind the comment which could easily be wrong.
If you do get one made up, I'm guessing it will be in flat laminated glass ? (years ago I had some windows made up from flat glass and that was all they could use back then) If so, I would make the window fractionally smaller than the template, maybe 2-3mm.
The reason is that I've just put mine back in and it really is a struggle. I used nylon trim tools to lever it in place, loads of soap and even WD40 at one point but even so there was a lot of shoving on that glass.
If it had been laminated glass then I don't think that has the same robustness as toughened glass. It's only 4mm overall thickness so that's 2mm either side of the central film and I honestly think the pushing I had to do would have delaminated the edges of a 4mm laminate. The depth of the rubber seal on the window side that I used was something like 5mm so it would stand a fraction smaller on the actual glass and hopefully make it easier to fit.
Brian