Using plumbing roof vent as drain?
Ideally you will not want to have your entertainment and eating space right next to the roof vent anyway. Noxious sewer gas will be coming up from there that may smell to high heaven at times. 

I cannot say if using the vent for a drain is acceptable to building codes. You will run some risk of water backing up into nearby sinks below if you start draining a slug of water down the vent standpipe.