Medical tape is going to have way too large a pattern for 1/24-25 kits. This is the best tutorial I've seen on the subject, and I think it's totally unrealistic. Do you want a vinyl or cloth headliner? As for me, I would use very thin plastic or card stock, cut the template as shown in the tutorial, and VERY lightly score where the seams should be. Or just score the seams on the inside of the kit roof. Then paint to the desired finish.
http://italianhorses.net/Tutorials/Headliners/hliner.htm