When I made my headliner out of the standard brown interior boad that can be bought at any upholstey supply shop, I first bought six or so pieces of poster board at the hobby store and I layed out my headliner divided into six sections. I cut each of the six pieces to fit in each of the six areas of the underside of the roof so when taped together they would cover and be the entire area of the headliner. I adjusted, cut and snipped until I had a good fit. I then layed the pieces on the headliner board and cut it to the pattern I had made. I over cut slightly so I would have a little wiggle room. When I installed it, it fit almost perfectly. I had to cut and snip a few spots, but basically I got it. That was back in the 90's and it is still right where I put it!
