[jnaas2]

Before you climb up on the roof go to the bathroom thats causing the smell and run some water into all the fixtures. Then have someone go flush the toilets in the other bathrooms and see if the drain makes a gurgling sound in the bathroom with the smell, if it doesnt then the problem more then likely isnt a vent problem. If you dont get a gurgling sound from the toilet or the sink I would say that the wax ring on the toilet has failed and its letting in air and also letting out the smell. If you know someone who has a combustible gas detector they can find the source of the methane smell coming from the sewer line