Make sure you DO roller in the same direction,if you dont it will look even worse than it does already.I am a painter on new build houses.We can do a newly plastered ceiling in two coats.Dont thin the paint,just put two good coats on and dont be scared of the paint just keep it flowing.If you stop and start edges will just dry at different times and will look patchy.Roll straight across from wall to wall and just keep moving backwards until the whole ceiling is done,give it 10mins and repeat.Deep pile are the best rollers to use as you get more coverage,also i cannot stress enough that no matter what people say crown is the best pain especially trade paint.Its the best coverage you will ever get.Hope this helps.