that is a REALLY pants way of changing the roof over mate! if only the outer skin was rusted, then you can change just the outer skin. a guy on here has done it to his S2 turbo.

even if you rolled the car as it was, the roof would crush but it wouldnt crush/snap off as much as it will now since you just weakend the whole effing roof!

oh well, your life in your hands/feet - literally!

good luck with it chap