My 1/2 cent worth, get a laser. If you are referring to clearing schools/business/regular sized rooms where you will be mainly shooting 6 - 30 feet the laser is ideal. If your build is for fun and not real life CQB/CQC, then maybe a low power optic will work for you. If you are really clearing rooms with unknown/multiple adversaries, you will likely be clearing with the gun mounted close to your chest center without bringing the sights upto your eye. An optic doesn't do much for you in this circumstance.
Dave