Q:

My roommate smokes marijuana basically everyday. He quit about a week and a half ago cause he has to take a UA at the beginning of January. Will everything be out of his system by then?

A:

Barely, depending on the concentration of THC in what he smokes and the frequency of use (sounds like it is frequent).

Just so you know, you have a chance of positive U/As for THC just from second hand marijuana smoke. Might want to consider a new roommate.