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 ...

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.

On Roblox, old and new coexist. It’s an interesting manifestation of the company’s ethos, and one reflected in the decisions Roblox makes with its underlying technology.