Open Roblox and sign in
Go to the Roblox Creator Dashboard
Select your experience or group
Open the Avatar Items or Clothing section
Download the official shirt template
Edit the template in an image editor
Place your design on the template correctly
Save the image as a PNG or JPG
Upload the shirt to Roblox
Name the shirt
Pay the required upload fee if prompted
Wait for Roblox moderation approval
Publish the shirt after approval
Set a price if you want to sell it
Test the shirt on an avatar
Fix and reupload if needed