It may not be the first time this has been done, but here's my attempt.
King of the Hill works really nicely for 6v6, but is a bit too hectic for a 12v12. To try and fix this, I've made a KOTH map with TWO control points. I hear what you're saying, "That's crazy, it will never work!" You're probably right. but I have to try.
Each team will have to split their efforts to try and hold both points. The timer only go down when both points are held by a single team. To win, both points MUST be owned by a single team. This means overtime could potentially last a while. As such, the control timer has been reduced to 2 minutes.
The upper point is a bit more open to favor jumping and ranged classes. The lower point is a bit more close-quarters to favor pyro and heavy.
Let's see how it goes!