Check out You Tube Matt's Off Road Recovery channel. His son Rudy has been upgrading his copper colored XJ known as "1/2 DONE". On (one) of the recoveries in the last 2 weeks (early to mid April), Rudy showed where he cut the KJ top and put latches inside to remove it when he wants to. They didn't go into much detail and it is not finished so I assume he will be posting more of it as progress continues.
Rudy also announced that he is starting his own channel (seperate from his dad and the whole recovery gang). It will focus on fabrication and upgrades. He will probably post the rest of the 1/2 DONE XJ work there including the removal top. Or drop him an email. Might be a good place to start. But be warned, they all do a lot of cutting, tacking and welding. But it might give you an idea of how to replace your roof. You also might want to look at some VW Dune Buggy forums. They do all things fiberglass and get ready creative with body mods. Another thought is a salvage yard like an old Bronco or Jeep with removal top. (IF) you can find a top large enough and with the right curves, you might be able to cut to fit and save having to make the panel yourself. But if you do the Rudy method (steel instead of fiberglass), you might have to cut the roof off a wrecked Liberty.
Back in the day, van lovers used to cut the roof off of a Vista Cruiser station wagon and weld them on top of a full sized van so they had the upper windows. If you grab a Liberty roof, it would be the perfect time to install an aftermarket sun/moon roof. I wonder if you can install a salvage yard headliner too? I would sure like to see what you come up with.