Users can create shirts by creating an image based on a template and then publish them using the shirt ContentBuilder. After being reviewed by a moderator and approved, the user then can sell or use the shirt. Only Builder's Club members can make and sell shirts, but everyone can buy them. The Builder's Club member can sell them for both robux and tickets.
A great program to use for shirts/pants is Paint.net, a free advanced paint program, because of its ability to make shirts transparant.Many users have published videos that demonstrate shirt shading using Paint.net or GIMP.