So, I realize that plenty of people may have thought up something like this before, but I haven't seen any posts about it (at least on the front page) so I'm just going to go ahead and say the idea that came to me.
Here's an image which is basically a rough sketch of what the maps would look like:

This gamemode would force players to take the tower unlike ever before. In the two existing gamemodes, a lot of people don't understand it's importance. That will change. The players that don't think they need the tower face the task of dealing with a ghost giant. But now, they would be punished by having to deal with three. This isn't as unfair as you would think because it not only would take a lot of time, but it is the players fault if they find themself sitting at the base building miners while the other player is already getting every tower and the tower spawns. In regards to how getting tower spawns to work could go two ways:

Or, It can be similar to passive income and stack up after each time you buy it. However, this would disable the player from choosing what tower they would like to upgrade.
Anyway, besides having the towers be claimed like you would think, it could be that you must get the tower closest to you before moving on to the next if that balances things a bit.
Finally, this gamemode is intended to be a little longer so if you feel that may be an issue, you are not forced to play and this gamemode wouldn't be for you. I personally like playing games that last a bit longer for pretty much every game.
Input is always appreciated and strongly encouraged this time around. Fire away!