Sans wrote:
Thanks for all the opinions.
How do I purchase good slate? by price, by brand? how do I know some
other tile store has the same one as HD?

I'd find a reputable tile (stone) store that carries slate. Tell 'em
what you need and let them help you select it. Then ask to see an
installation where the recommended slate has been installed for some
number of years in an application similar to yours. That should do it.
The HD slate separates and crumbles in a matter of months, not years,
especially in a wet environment.