Hi,
We have submitted a new app to shopify store by which you can design any type of product from admin, customers can modify the product design from admin (if any) or can create his own design and buy it on the site!
Please check the demo here: http://custom-product-design-studio.myshopify.com/
The installation url for the app is: https://apps.shopify.com/custom-product-design
We have 7 days free trial so that you can install and check it out.
Thanks