Can roll top ridge be scribed?

This depends on your location. In Queensland all ridge and hip flashings are scribed – or cut by the installers, onsite – to suit the cladding they sit on as this gives maximum protection from the rain. In other states, the capping often (but not always) simply sits on the top of the corrugated cladding. You can buy Retroseal Ridgeseal from ShedBlog to seal gaps in a ridge.