When building a bird bath, your imagination is the limit. You just have to obey some guidelines, that are vital if you want your bird feeder to be safe and useful to birds.
In nature birds prefer puddles to freshen up. That means your bird feeder is going to have to mimic a puddle to be attractive to birds. Round, shallow containers are great for that purpose. You have to make sure the container is not deeper than 3 inches, birds like shallow water.
You can use a large clay pot saucer on the ground, that is one of the easiest homemade bird baths. But you have to be careful when you choose a location for that ground type bird bath. Predators can be dangerous in that case.
It's generally safer to put your bird bath on something taller, so predators can't get close as easily. But you have to make sure you choose something that is heavy enough so birds can't tip it over. An old stump or a concrete block will do just fine.
If you want to make your backyard birds feel like home, put some smooth rocks or some gravel in your bird bath before you add water. It helps the birds get a secure footing.