Alright, so here's what I'm envisioning right now. A future world where human kind has begun to conquer the closest planets to us. The map would be relatively small, only going so far as, say, the Oort Cloud. Most planets, except the four inner ones, would be a single Supply Center with some moons serving as SC's as well. (And we can, of course, include certain comets or meteors that aren't necessarily planets, but would provide tactical resources as SC's.) The Asteroid Belt would hold a few SC's, but would mostly serve as a buffer between the planets. The main countries would have their home SC's focused on Earth, Mars, or the Moon, and would include an outpost or two on a far away planet such as Saturn. For the most part, armies would remain on the Earth, where people fight over their home ports while others attempted to conquer more distant planets and to leave Earth behind. The fleets would travel through space and convoy armies around if needed. (Build anywhere would seem like a good idea.) Only armies could conquer SC's, but fleets could occupy them for the sake of protection...and yes, 3-D would be epic.
Nevertheless, I am not in charge here, you all can do whatever you want.