The "chopped" sedan must be drastically changed to provide the undercarriage support that a convertible has to have and also to provide for the placement of a folding frame for the convertible top. This is such a major job that it is just not feasible. There are still restorable convertibles out there. Find one to bring back to life rather than attempting a conversion. There are sunroof conversion kits out there that work. There are a lot of shops that specialize in this sort of work too. Just remember, you will no longer have an authentic Beetle sedan. And replacement parts for the custom sunroof, if necessary, can only be obtained from the shop, or its supplier. We do not have parts for any of the custom sunroof cars out there. We have original sunroof (by Volkswagen) parts to repair original Volkswagen sunroofs.