As a Roblox developer it’s currently inaccessible in mobile to create t-shirts and other clothing.
The Problem
Some people these days are now into mobile devices, and some Roblox users who can’t access computer devices can’t create t-shirts in mobile.
Most users who are abroad, going to another place, should I say, have a broken computer or laptop and are mostly using their mobile devices can’t access this feature and mostly they take this very frustrating because of the inconvinience.
Solution 
Roblox should add a feature where players and users could upload clothing in their mobile devices because as we know, most Roblox users really love to create t-shirts because of the fact it’s their own design accessory for their avatar.
This would also help the users who love to create t-shirts to make it more accessible and faster because when creating t-shirts in mobile, it’s sometimes easy to design this via photo editor apps.
It’s also more easire to create t-shirts in mobile because people can edit photos there through a simple photo editor,
or a free photo editor like SnapSeed or AdobePhotoShop. To be honest, also, it’s more easier to edit through mobile, because photo editing in mobile is in touch-screen and we could agree that’s more easier and faster. This would also make people get a faster job in designing t-shirts to sell them in the community.
Conclusion
If Roblox could address this and maybe add this feature, it would really help mobile users who can’t access computer devices to instantly create t-shirts and other clothing even though they’re in a vacation, or have a broken computer or laptop, this would also help make the clothing upload become more faster because of the use of mobile devices.