The way my game would work you would either build your own base, or your team would make a base. You would have a certain amount of money to do it with. You have a certain amount of time to build it without interruption, and then the game starts. You can either choose to continue to build, go on the offensive. Objects you can use to build your base would be walls, shield doors, weapon spawns, towers, teleporters, defensive emplacements, vehicle spawns, or structures that give you support abilities. Each map is divided into zones, each zone being selected at start as being your territory. You get a map, of which there are two types. Balanced and unbalanced. On a balanced map, each zone is more or less the same, with the same advantages and disadvantages. The zones on an unbalanced map, however, would be wildly different, but you would get extra money/build options if you choose the less favorable zones. For example, one zone could be set upon a hill near the edge of a map, out of the way of other players, with only one or two natural entrances. However, you would get little money, only able to put the bare basics down, such as machine gun nest to cover the entrances and a small outpost to cover the necessities. On the other hand, one zone would be in the middle of a map with no natural barriers, in a depression. But at the same time you would get lots of money, enough to fully fortify, along with some sort of special support or vehilce. The hardest part would be to balance this, because otherwise people will always try to pick one side of the scale, and whoever is on the other side will be hopelessly outmatched. Once you do that, there are several ways I see the game being played-
Individual vs Team- If it was a free for all, then you would want to make it hard to get into your base, possibly by the use of some puzzle or secret entrance. You would want to wait for the other players to get out of their base, and then try to sneak in. Or you could blast your way through any defenders that are there. If it is team based, then you would want some of your team to keep guard at all times, while the other team members go on the offensive.
Objective vs Kill count- If it is objective based, then there would be some object in the other player's bases that you would want to take or destroy. This could be a flag, or a generator you need to destroy. If it is based on kill count, then each base would provide vital support to each power, such as more powerful weapons and vehicles, or the ability to call in airstrikes or artillery. You would raid bases to take these out, and defend your own to keep the same from happening to you.
This is based on when me and my friends from middle school would play Forge Mode on Halo, building our own bases and trying to kill each other at the same time. I remember there was this one time I made a complicated teleporter network that you needed to go through to get to my base. Which is where I kept all the awesome weapons.