O.K. here it is until Demis add it to a full tutorial. I suppose you've add an navy-admin slot in Athens with
Demis' tutorial and you've given the right coordinates with
erasmus777 excellent sheet. Now do the following:
In main/startpos.esf go to CAMPAIN_STARTPOS/CAMPAIGN_ENV/CAMPAIN_MODEL/CAI_INTERFACE/CAI_WORLD/CAI_WORLD_BUILDING_SLOTS. Clone one of CAI_WORLD_BUILDING_SLOTS (whatever you want), and put these numbers :
In CAI_WORLD_BUILDING_SLOTS first line put 9999.
In CAI_BUILDING_SLOT first line the navy-admin building ID you have made, second line put 0 (thats the group ID for buildings inside settlement), and third line 1681 (it's the the table of Athens in CAI_WORLD_SETTLEMENTS). Thats it! Enjoy