Automated Website Setup - Multisite?

Hi,

I am looking to setup a site where users signup, pay subscription and wordpress auto generates a website template for them that they start building on - ie; fill in the blank pages, add photos etc.

How do I go about doing this on Wordpress? At present I am currently doing this manually for people who sign up. However, I would like this to be auto generated for anyone who signs up.

Any advice would be great!