Slate roofing is typically considered a more expensive type of roofing material. The material itself costs more, it takes longer to install and some slates, being thicker, require a stronger supporting frame. If it's well constructed, a slate roof has a normal life expectancy of more than 50 years. A slate roof is also fireproof and waterproof. Slate requires very little maintenance and never needs any kind of preservative. The inspector will check for proper installation and any signs of defect. If shingles need to be replaced, it is important to use a slate that is compatible with the original roof.