+1 on the autoglym
I have said this before and i will say it again, as you are seeing a roadster if there is anything wrong with the roof at all just walk away.
Any misalignment or catching of windows on material, or any tears or leaks just walk away. It will be complicated and expensive to fix. I have seen lots of posts by people that got caught up in the moment and bought a car thinking a minor issue would be ok. Don't do it think with your head (which i know it difficult when you turn your key and start it up).
My old 350 had a minor leak on one window and i thought ah they can replace the rubber. It was very expensive (they paid) but the problem still occurred and in the end its the reason i sold the car. Make sure you get a gem