On your car, this is major surgery. You will need a good sheetmetal welder, and a person to cut down the windshield, and make some new side glass.

The very best way is to have another body to rob pieces from, because as the top goes down, the edges will spread farther apart, so if you have a second body, you can use the two cars to create a new roof, wider and longer than the original.

This probably is best hired out to someone knowledgable in major body restyling. I haven't been involved in this in many years, so I can't even tell you what an approximate cost is to have it done.