A four-story building along the 16th Street Mall is the second in downtown Denver to be recently eyed for a potential office-to-residential conversion — something that the city is looking to encourage. Kresher Capital, which owns the building at 1600 Champa St., submitted plans for the conversion to the city last week. The plans call for the top two floors of the building, currently office space, to be fashioned into a total of 40 apartments, ranging in size from 470 to 1,135 square feet.