I have always been told that it is better to vent toilets at roof level rat?

I have always been told that it is better to vent toilets at roof level rather than use a dergo valuve, could you please advise if this is the case as I would perfer to vent a toilt on a project that I am working on with an in line vent but the buiding surveyour is recommending an external air intake valuve. I would appreciate another opinion.