Here was my set-up:
Map: War Machine
Players: 4 (Engineer, Scout, Heavy, Sniper)
If you are familiar with the War Machine speedrun that is most commonly used for Re-Up 11, this is the same thing. In fact, it's much easier since it's not Inconceivable and Ironman was not turned on. If you're not familiar with it, here's a quick run-down.
1. Place fabricator upstairs, all the way back in the middle section (the small hallway)
2. Start with 1 sentry & 1 barrier
3. Save up for a 2nd sentry and then a 3rd.
4. Let sentries do the work while you provide support.
5. Occasionally build a Shock Sentry + Locker
6. Repeat steps 2-5.
If everyone has good cards, you can do this with 3 people (engineer, scout, X).
I would still recommend a 4th depending on everyone's class' skill levels.