Longevity:
When the 100 year+ life of a slate roof is considered, the value of the investment in slate becomes clear: This will be the last time in your life you have to worry about roofing. Also, if you have a home that you plan to keep in your family, future generations will thank you!

Slate is fire-proof:
As a non-oil-containing rock, slate is completely non-flammable. No matter what heat it is exposed to, slate will NEVER burn. Not only is slate great for keeping water out of your home, but it will also provide you another protection against house fires
Insect and Rot Proof:
Slate will never succumb to rot, insect, or pest damage. What else can we say about that? Impressive!
Slate on a New England roof
Greenstone's 100 Year Warranty:

Greenstone Slate Company, Inc. grants a 100-year limited warranty on all slate roofing materials supplied to its customers. All responsibility and liability of honoring this limited warranty is solely that of the above mentioned and covers the Delamination and Substantial Deterioration (softening)