How much paint do I need to apply to a new Shurline roller at the beginning of a paint job?
Shurline roller covers are a mid range quality cover, but not bad and should do the job fine. I like to use Purdy White Cloud covers for final coats.  If you are getting lots of ridge lines, that usually indicates that you are pushing too hard on the roller and trying to stretch the paint. Don't be afraid of loading the roller, obviously, you don't want it to be dripping, but don't work too much out of the roller before you start to apply the paint.  If you find yourself pushing harder to transfer color, then you need more paint on the roller.  Also do smaller sections at one time, not much more than a 4ft by 4 ft. Cover an area wall to wall one side to the other, then make one continuous long stroke over the entire length softly to even out the paint and remove ridges.  Keep in mind, especially with cheap ceiling paints, the first coat always looks spotty and should improve with second coat.