First of all, this is not vinyl like is on your car seats, it is a special vinyl to withstand being on the roof of your car. The top usually has two seams on it that are sealed to prevent leakage. The seams are there, because Landau topping is normally 49" wide and won't cover the entire roof in one piece. Landau Vinyl Roof Covers
This is not an easy job, and is best left to a professional with the right glue, equipment, and experience.