Create website with specified features to link with my Shopify e-commerce store

This project will require a programmer to create a website (for each of my customers to generate PDFs) that I can use in conjunction with my Shopify e-commerce store. I will go into more detail and provide more of my ideas once I've hired someone to complete the job, but the most basic outline of what I need is a site that allows me to direct a customer there from Shopify in order to actually make the product they are going to purchase, and then link back to Shopify for placing order(s) and payment. (Really, the goal is to have a customer create & save a PDF full of their own selected content and place an order for purchase via Shopify in as few steps as possible. We'll discuss this.) I have some hand-drawn wireframes and notes to share, but the site to be built will consist of a few pages (likely not posing much of a programming problem) with photos, links to social media, and instructions on what users are meant to do, and then the core functionality: creating a means of compiling and storing a customer's favorite textual information in the form of a PDF. This will be put into a book-like document, with a few limited cover/color and size choice selected by the customer. The site must be user-friendly and fit in with my Shopify site's color scheme/theme, leading to an attractive overall user interface and shopping & creating/curating experience. The programmer will use Github so I can see code along the way and after the project. The document created by the user will need to be stored and accessible at a later date by myself or the customer. After a customer has created what will become the product, I will send it to a print-on-demand publisher for printing. I will explain what my goals are for this project via Skype or Screenhero so you know exactly what I need.