If you want to dive into the fun of brush creation, I can, no, I have to, recommend to you the series of videos on the topic created by @RamonM, currently I don’t know a more comprehensive guide into brushes and the way to create them yourself as this series!
For the kind of brush you want to create, you may try it with a masked brush, where you probably want to use a mask of a different size than the main brush tip. Maybe it is worth to download and inspect the so-called hollow or outline brushes you can find in the sub-category Brushes and Bundles of our Resources category:
By the way, this kind of brushes can also be found in a few bundles.
Michelist