Yes, slate is an expensive material to purchase, time-consuming and expensive to install, but a slate roof will last for a century and more with proper maintenance. Considering the long-term value of slate, it is probably the least expensive choice for your roof. An asphalt roof will need to be replaced every ten to twenty years, but your slate roof will only require minimal maintenance every twenty years or so.
We purchased the material for this roof from Vermont Slate Depot. We chose 10 inch shingles. The cost for this roof came out to about $4.5 per square foot. A larger roof, with fewer cuts needed would come out to be less per square foot. We used galvanized steel nails to prevent any possible corrosion stains from appearing. The ridge cap and valleys are Galvalume, a material made from a high-percentage of post-consumer recycled metal.
This roof has a slight curve at the sweep–which made for a bit of a challenge when in came to installing this super rigid and brittle material. We visited a number of local chapels with similar pitched roofs in upstate New York to research how to successfully pull off this trick.
Slate will absorb heat to give you a much cooler attic in the summertime and will slow/prevent heat loss through the roof in the wintertime.