Two people that I would recommend to do a roll cage......one has already been mentioned.
Another would be Ted at Creative Motorsports. 352-588-9621 unless he changed it.
He built an SCCA Beetle for his first driver's school years ago,
and now builds cages for cars that race the Daytona 24 Hour Race.
He knows how to tie in the mounting points for maximum handling and frame stiffness.-Bob