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.

Roblox is an online gaming platform and a tool for game development created by the Roblox Corporation. It enables users to create games and play those that are made by others.

How to share your Roblox games with other players How to start creating Roblox games You create Roblox games using Roblox Studio, a free piece of software you can access via your Roblox account.