A question about masking tape.....wouldn't the adhesive give out over time and break loose from the model? By "over time" I mean like 10 years or so. My dad was one of those guys that made every repair around the house with masking tape (these were the years before duct tape) and the stuff seemed to dry out and break away from it's intended repair.....usually keeping the shape of the "repaired" item. Heat seemed to be the culprit.
I'm by no means a detail master, but I've had good luck using tissue paper.....the non-embossed kind (you wouldn't want faint flowery patterns on your roof). Use single ply.....usually "Macho Wipe" works well...that's the kind that simulates sandpaper. I accidentally picked up a pack of that, instead of the fancy soft kind, and it was banished to the garage (along with myself for a time). I now have a lifetime supply of vinyl and convertible tops. Worked out well in the end.
What I've done in the past is thin out white glue and lightly brush or pour it over the tissue placed on the roof. It's easily trimmed away once dry and a coat of paint will help lock it down even more. Wish I had some photos to prove my point but I've also used this to simulate canvas on 1/350 ships. The one down-side you get, as opposed to masking tape, is that once it gets wet it's VERY fragile and will tear if you so much as look at it harshly.
Just my two cents.....
Matt