Freeradius + OpenVPN Solution to Traffic Limitation

[ToriTori]

I need to limit the monthly traffic of OpenVPN users on my server. Example: After a 50G/month traffic limitation has been reached, the server will disconnect and reject connections from that user for that period of time.

Everything seems to point out to Freeradius as the best solution! I'm just having problems finding any guidance to achieving this.. could someone please instruct?

Thank you,
Chiappa