Slate tiles are favourable for eco-friendly roofing because they are highly resilient and long-lasting. Slate is a natural material which has withstood the test of time. Therefore, the roofing system created with the tiles will be able to withstand mechanical stress from snow and other adverse condition. The tiles are also naturally resistant to heat, so changes in weather will not have an adverse effect.
Though the purchase price is high, you should note that slate tiles are extremely durable such that most companies will offer up to 100 years warranty. This aspect means that if you install these in your home, you will not need to replace in the foreseeable future. If you can find a company which repurposes old slate tiles for new roofing, your home will be even more eco-friendly.