Inspect problem roofs to determine the best repair procedures. Remove snow, water, or debris from roofs prior to applying roofing materials. Set up scaffolding to provide safe access to roofs. Estimate materials and labor required to complete roofing jobs. Cement or nail flashing strips of metal or shingle over joints to make them watertight. Install partially overlapping layers of material over roof insulation surfaces, using chalk lines, gauges on shingling hatchets, or lines on shingles. Cut felt, shingles, or strips of flashing to fit angles formed by walls, vents, or intersecting roof surfaces. Apply plastic coatings, membranes, fiberglass, or felt over sloped roofs before applying shingles. Install, repair, or replace single-ply roofing systems, using waterproof sheet materials such as modified plastics, elastomeric, or other asphaltic compositions. Attach roofing paper to roofs in overlapping strips to form bases for other materials. Cover roofs or exterior walls of structures with slate, asphalt, aluminum, wood, gravel, gypsum, or related materials, using brushes, knives, punches, hammers, or other tools. Waterproof or damp-proof walls, floors, roofs, foundations, or basements by painting or spraying surfaces with waterproof coatings or by attaching waterproofing membranes to surfaces. Apply reflective roof coatings, such as special paints or single-ply roofing sheets, to existing roofs to reduce solar heat absorption.