So can I take a back door off a 4 door and the rocker panel to make a patch panel on my coupe? I have never done any body work ever.
While I love to see someone go for it and learn, you might want to start with a simpler repair or two and work your way up. How's your welding skills?
The rocker panel section has a nice shape to it that would be helpful in the repair. I'd use it and I'd just make the flat pieceabove it separately. The door bottom isn't really going to help.
What Tinbender said. That isn't too hard of a panel to make yourself with just hand tools though. Spend a little time on Metalmeet.com and Allmetalshaping.com and practice on some scrap a little first. Welding is going to be the hardest part if you've never done any, but it is as much about confidence as it is about skill....
Seeings as how your coupe is being held together by straps and wires, I'd say you're a long way from choosing a patch panel! Once you get it all apart you may find you need something completely different.