If I would make one, I would like to see:
- Long docks, sufficient enough to also dock big ships.
- a Jail
- a Bar
- Barracks
- Officers place
- Enough cannons
- Cliff's
- Palmtrees, and other vegetation
- Maybe a cave with a sea entrance
But above all; the shape of the fort needs to be logical, they wouldn't just pick a random spot and start building. It has to have to strategic capabilities.
Like this one:
http://www.flickr.com/photos/45244184@N04/4339804395/in/pool-forbiddencove