Create a Roblox account
Get Roblox Premium
Open the Roblox Creator Dashboard
Go to the Creations section
Select your experience or group
Choose Avatar Items or Clothing
Download the official Roblox clothing template
Open the template in an image editor
Design your shirt or pants on the template
Save the file as a PNG
Upload the clothing file to Roblox
Name your clothing item
Pay the upload fee if required
Wait for Roblox to review and approve it
Test the clothing on your avatar
Publish or sell the clothing item if allowed