Customize plugin for woocommerce subscriptions

I am using wordpress 4.0 multi site configuration with the Woocommerce plugin and the Subscriptions add on: [login to view URL] For my membership option within woocommerce subscription I need a field added to the subscription checkout page that allows a user to input their site name: for example [login to view URL] -- so the customer would only enter "mysite1" as [login to view URL] would be pre-filled in for them. Once they have completed checkout their network site would then be created automatically. I also need it so if they ever cancel their subscription the loose access to the site.