Built on Roblox's real 585×559 classic-shirt UV template (pixel-verified against Roblox's own official download, not guessed). Pick a base colour or pattern, drop on your logo, text and shapes, then export a PNG that's ready to upload at create.roblox.com under Avatar Items > Shirts. Nothing here is uploaded or saved anywhere unless you save it to your account: it all happens in your browser, and the guide lines are for editing only, never part of the exported file.
Drag to orbit, scroll to zoom. This is a simplified stand-in body for previewing placement, not your actual Roblox avatar.