Are you considering getting into the custom T-shirt business? T-shirt design is a booming industry with many possibilities for making extra money on the side. If you are interested in starting this side hustle, you can either create your own brick-and-mortar and purchase the materials and equipment you need or use a third-party service to print and send your designs. Many websites will allow you to design T-shirts and sell them on their sites. These sites include Zazzle, RedBubble, Printify, UberPrints, and TeeSpring. Most of these companies do not need an upfront cost. However, you may need some design products.