fabricating the vert would greatly effect the safety of the vehicle. basically it becomes a death trap with no resilience to rolling over and crushing you... very bad idea IMHO. Modern convertibles are very hard to roll for a reason... they are engineered this way, its one of the reasons (as far as I know the most important reason) why they weigh more.

 

This is a textbook Boondoggle, <-- look it up. Anything is possible, but to make it work, to ensure all the parts come together seemlessly and weather tight is a daunting task.

If you really want a convertable, as said already. Just chop the roof off, add some strengthening beams and finish off where the roof was. No sense in trying to make a top. Just watch the weather report.