It's such a great idea for a simple wall treatment. I used this very same method (with a plate) to make scallops for a window treatment. Another way of doing this is to make a template out of cardboard with a plate. Karla describes the process:
You will need:
a level (a long one),
a pencil (or something to mark on your walls),
a saucer (or a round object that fits the size that you want your scallops to be),
and painters tape
a level (a long one),
a pencil (or something to mark on your walls),
a saucer (or a round object that fits the size that you want your scallops to be),
and painters tape