If your going to get a roof off a parts, car take it apart and put it in your car piece by piece. If you just cut the pillars and weld on the new one you will lose alot of strength because there are several layers of metal in the pillars and you wont be able to penetrate all those with a weld. I'm just finishing up a roofskin replacement on a challenger that had a vinyl top. Those things are killer on sheetmetal. Good luck with your project. Stay focused and before you know it you will have a sweet Charger!