I do the overlaps of the vinyl by laying down masking tape, leaving a thin gap where I want the lines then spray with filler primer, about two coats no more than three. Texture then is done by holding the rattle can, semi black or whatever colour you like, about three feet away. The particles almost dry before they hit the roof, a few coats like this keeping the can about three feet away gives the vinyl roof texture. I've used this method for years, though on 1-1 car parts like dashboards, but works just as well on model kits.