Lately, a lot of kids are into expressing their personality through phone cases. What I like to do is design my own using nail polish and/or glue along with some other random supplies.
I buy plain, solid-colored cases and decide what I want to do with them. I normally paint a base design such as stripes or dots with different color nail polishes. Then, I use nail polish to paint a quote or a saying on the case and accent it with other colors. My favorite tool is a black striper brush I use to paint quotes for most of the cases. It's actually really hard to get the letters or symbols to look good using only a brush.
Other times I glue different things that I find around my house to the case such as googly eyes to make an EYE-phone case. Its fun to just be creative with everything, and it's amazing what you can do with a little nail polish.