It looks like roviewer is down. However you can use the BloxMake Clothing preview tool to preview your roblox shirt and clothing designs. Click here to use the BloxMake previewer.
Roviewer was great because it did generate a 3d preview just like the BloxMake previewer. Some complained that the roviewer tool used up too much CPU, but the BloxMake previewer is fast and does not use any CPU to generate your preview.
Is very important to preview your roblox clothing using a preview tool so that you can catch any inconsistencies or issues with your design.
Everyone in that game is wearing the same catalogue clothes. Describe the outfit you want instead — Studio designs the shirt and the trousers, then shows them on a Roblox character before you download.
Or browse thousands of ready-made Roblox shirts and trousers — free to download.