than walls, because you only have the edges to cut in. Rolling over you head can be splattery, but I have found that if you get a good quality roller cover about 1/2 inch knap and an extension pole that is sturdy you will knock this out quickly. Splattering does occur with pait that is often too runny and most of the time occurs when you apply or roll the roller too fast.
The shield that one suggested is a wise investment, but if you tarp, as you should it really does not matter.
Remember the sequence in rolling to allievate the roller marks and thickness of paint problems.