You dont say if the files are downloadable only, but..
I recently had a similar situation where whilst running a real estate site and giving access to contract,inventories etc was a need between the client and landlord, giving only access to these whilst relative to the post(property) in question.
I ended up with what I think was the quickest and most robust choice by installing the WordPress Download manager Download Manager.
Using it you can then set up a function in the relative page giving access to the shortcodes by user role.