Return report as from customisation via rest api

Hi all

Perhaps a case of running before I’m walking here and quite probably missed some step in the docs/examples. 

So what I’ve done is develop a customization which I intend to build an extension library from. In this customization I created a report (This report is kind of like a Purchase Order).  Now what I want to do is to via a rest service call where I pass in a record id, download this report as a pdf.

In the customization I think I’ve got the method sorted to generate the pdf document, but I can’t figure out how to wire up a service endpoint to trigger this method and return the pdf.  

Are there any examples around I should be looking at?  Or advise on how to do this?