Thanks, definitely thinking about it. Dont suppose you could send me some pictures? What spec is your car? Standard or modified (if modded, how much)?
If it happens on the standard roof, then all I am doing is putting off the inevitable. Is there actually a fix or do you just accept it?
Matt's car is an HSCC 70s Road Sports race car. So with the associated permissible modifications (relatively limited compared to what people might do if building a hybrid Z) - its not like he's tweaking the shell with a 400hp+ RB or something.
I'll add another voice - from the perspective of a road car driver - about the flex. They most definitely do, even just when engaging in "spirited" road driving. It's one of the reasons strut bars are a popular bolt-on mod as they do actually have a positive effect.
Thinking about the roof specifically, its not totally unusual to see the occasional car - even road cars - with some evidence of shifting or paint splitting where the roof joins the rear quarters (the factory leaded area). Albrecht mentioned this above. That's a good indication of movement/tension in the roof area. When I rebuilt my car (after an accident that caused roof damage - see my gallery - pale compared to what happened to racer's though!), some rust repairs were done to the areas above the quarter glasses at the roof to quarter join, with new metal let in. Some skimming was done post metal-work and recently I noticed on one side, in the right light, that you can now see the join line between quarter and roof. Very minor and anal but indicative to me of some shifting or shrinkage occurring over time. And that's a tiny area in the periphery. Heavier skimming for shape over a sunroof patch is much more likely to become apparent a few years down the line. And its such a visible area - your eye is drawn to it and imperfections in it.
I think Alan made a very good point - there are many other areas of attention metal-work-wise that the bodyshop needs to focus on, which would give you a time window to explore sourcing a complete roof skin. To quote Hicks in 'Aliens', "it's the only way to be sure".
Balance your understandable desire to get the car on the road and enjoy it with the dictum "do it once, do it right".