Gamers can customize their avatar by creating clothing, like shirts and ... For each template, notice that the parts are "folded up" and wrapped around a Roblox character's body, arms, and ...

On the Roblox website, there are several templates. One can use those PNG files, which have a transparent background, as inspiration while creating the design for the shirt.

so you'll need to design a t-shirt in an image and then upload it to Roblox. From there, just select it to wear and you're sorted! You'll be best off having a couple of templates for this!