Helping buyers with information about the roofing materials and it's condition should be directed to a roofing expert for inspection.
I have found that composite shingles are the most commonly material used. The lower-end, three tab shingle vary in life ranges of 15 to 20 years, where heavier and more expensive architectural shingles give a textured, three dimensional look. The life expectancy is 30 plus years for the higher grade shingle.
Clay,tile and slate are stylish and more unusual. The cost is also expensive and takes longer to install by a experienced seasoned contractor. These type of materials heat up slowly which provides a more moderate effect on hot temperatures. Tiles are lighter than concrete, but more fragile. Both these materials can weather years beyond the life expectancy of traditional asphalt/composition shingles. An estimate maybe of 50 plus years.
Metal roofs are becoming more popular. They come in a variety of textures, shapes and thicknesses. Composites can look like wood shakes to slate and can be pricey. Life spans can reach 50 plus years.