Customized items in a webshop

We need a website that allows users to build own customized graphics on certain items (mug, t-shirt, carpet, etc.). Certain elements (text, images, etc.) have prescribed properties (size, place on the subject), but in this context the users might realize its own ideas. As a result, exported to a PDF, a preview in 3D, the user would have to confirm it, then in the online store the opportunity to buy, for example, via PayPal. The printing company receives a "print ready" image. About all steps occur logs and users and administrators would get mails about the order status, etc... Please describe the method you would use to make the software.