If you're building a room within a room, you don't need to make the roof heavy. The double layer of wallboard on the ceiling will suffice. I think you gotta ask why you need sound reduction. Is it to keep external sounds from getting in, or your cranked guitar amp from getting out. Either reason can be mitigated with planning and thought and an open mind.
The whole idea of concrete beams and tiles on the roof seems over the top.