It would be nice to have an easier way to set the roll. This is one thing that usually needs to be adjusted. Right now the workflow is just to keep resetting the roll, clicking OK, and redo, until you are happy. I think a first step would be to have an "apply" button in the dialog, so we can see the change without having to close the dialog. A much better method would be to have a "horizon tool" that would allow you to draw a line on the horizon and have it calculate the proper roll.