Don't write code that's already written.
The rails-stripe-membership-saas application is on GitHub.
Generate an app in minutes using an application template:
$ rails new rails-stripe-membership-saas -m https://raw.github.com/RailsApps/rails-composer/master/composer.rb -T
You get a complete membership site with recurring billing for your web startup.
Get the ebook from Giles Bowkett for an excellent code review with suggestions for improving the application.
Do you prefer Recurly for billing? There's a rails-recurly-subscription-saas application.