In my comment I said we looked into metal and other materials, but all increase weight, requiring engineering evaluation of the house and likely reinforcing the structure. Ceramic and concrete tiles are common here, but have the same problem. Don’t know about slate, but for the tiles you mention underlayment still needs to be replaced every 20-30 years at least requiring these to be removed and reapplied. Since labor is the major cost driver, it’s basically like paying for a new roof.