Companies were dispatched for the working bldg fire. Arriving units found a large 1 story commercial bldg, irregular in shape. The section involved was approx 30 x 100 with fire in the roof area. Crews had 4, 1-3/4 water lines in service with truck co's on the roof opening up. The bldg was a bldg supply house. Crews kept the fire in check from spreading to the rest of the bldg. Keeping all fire damage to the front of the bldg.