Chimneys, dormers, valleys, skylights, etc., invite problems with flashing and make reroofing difficult. Multiple layers, each known to be imperfect, offer protection that one layer striving for perfection cannot. Wood shingles last only ten to fifteen years. Composition shingles last about five years more. They are also fireproof and beautiful.
Concrete tiles lack the beauty of pottery tiles but are cheaper.
Slate doesn't last as well as tile under the combined influence of sun and rain. Since architects began being sued for leaks, metal roofs have increased in frequency. Stainless steel and copper are the leaders. After the roof, the windows are the most vulnerable. The catalog of problems presented by windows includes cavities and seals, condensation and moving parts.