For an idea what the C-office might look like, see the photo linked below. Basically, it is where the aerodrome authority resides, operating the radio, cashing your landing fee, keeping the a/d logbook, answering the PPR phone calls and/or faxes. Normally it is the first place where one goes after landing, to make sure all local rules are satisfied.
http://mw2.google.com/mw-panoramio/p...m/89462118.jpg
http://www.rvg.be/Picts/tower2_s.gif