To create and sell avatar items on Roblox, start by designing the item. Use a third-party image editor to create your design. For shirts and pants, use specific templates to ensure they fit avatars properly. T-shirts should be 512×512 pixels, while shirts and pants need templates with specific sizes for different parts.
Next, upload the item to Roblox. Go to the Upload Asset page and select the asset type (T-Shirt, Shirt, or Pants). Click the upload button, choose your image file, and enter a name and description for your item.
After uploading, test the item in Roblox Studio. Open the Avatar tab and click Rig Builder. Choose a rig type and insert the clothing object (ShirtGraphic, Shirt, or Pants). Apply the uploaded image to a dummy character to see how it looks.
Finally, sell the item. Once approved by Roblox, it will appear in your creations. You can equip the item or list it for sale on the Marketplace. If you need help with design, websites like CustomUse offer templates that make it easy to create clothing items without design skills.