If you notice foul sewer gas smells coming from your shower drain, the problem may be easier and a lot less costly to solve then you think. If there is no problem with the drain being slow, that is the water flows freely and doesn't back up into the shower while you are using it, the problem could simply be that the inside of the drain is dirty.
First remove the two screws holding the drain cover in place. These are small, short screws and you should relocate them somewhere outside of the shower so that they don't roll into the open drain. With your screwdriver and a little bit of pressure, you will be able to pry up and remove the drain cover.
Soak the paint roller cover in the bucket of cleaning solution and then place it into the drain opening. You should be able to insert the roller cover deeper into the drain using a gentle, back and forth, screwing motion, scrubbing the inside of the drain all the way down to where it meets the trap. Remove the roller cover and repeat the process until you can see that everything is good and clean.
Replace the drain cover, re-insert and tighten the two fastening screws, and you should be good to go.
If The Odor Returns
If the gas odor returns within a short period of time, you will have to use a different cleaning method. Sometimes organic materials (soap, sweat, dead skin cells, etc.) build up and actually accumulate in the shower pan, which is the base of your shower, located under the ceramic tile. Your tile grout is porous and over time begins to allow materials and water to penetrate it. If this happens, the odor may be imbedded in the shower pan and not the actual drain itself.
If odors persist after these cleaning efforts, it may be time to contact a plumbing professional.