I'd like to convert (and finish) the back section of my 2-car tandem garage into a separate utility room. This would involve 4 walls and a floor. 2 of the walls would be attached to concrete walls, 1 would be attached to existing house/garage wall, one would be new to separate front car space from rear utility space. My concrete slab garage floor is sloped towards the center to allow for drainage into a sewer pipe.
How do I frame everything to be plumb and level when the garage floor has slope?