Much like most things on Roblox, you will be making this yourself from scratch, so you'll need to design a t-shirt in an image and then upload it to Roblox.

To start, check out these handy templates which ROBLOX themselves has created. If you right click and save these images, you can use them as a guide on how the clothes should look once you upload ...

Roblox provides its users with a wide range of options for personalizing their avatar or character. Players can purchase or acquire free items such as clothing, accessories, and other cosmetics.