Website Subscription via PayPal

I am looking to build an application on PHPRunner which I will charge a monthly/annual fee.

Does anyone have experience in doing this and can put me right?

So process would be (simply put): -

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1. Customer registers on site.
   
2. If customer has not previously paid then they are offered Pay option or no further progress.
   
3. If customer has previously paid then they can log in and get full access.
   Thanks in anticipation of your help.