I only remember one restaurant at Great World City where I don't think there was any charge for the private room, just need to book and request for it. Wasn't on my tab though, so please call to check or something:
The room I was in was pretty small, definitely cannot fit twelve but I am pretty sure that they have bigger ones, unless my memory serves me wrong. The layout of the private rooms also a little bit cramped, though you get privacy, well.
Food was so-so in my book, and well, it's the standard Crystal Jade fare, not sure if it fits in your book but it's all I know, hee hee. Please don't kill me if it's too low for the class, not being sarcastic or something.
You're asking at the wrong time of the day I guess, not many replies now, maybe wait for night.