[PaulDavisThe1st]

There is very little acceptable roofing slate available in the USA. PA has a few quarries that provide it, but according to roofers (in PA) that I talked to, it is still nowhere close in quality to, say, Welsh slate. Too many voids which when coupled with much more severe freeze/thaw cycling in much of the USA leads to early failures.

I think you may be overestimating the extent to which UK houses are held for "generations.

[bombcar]

And even if you import Welsh slate, you may have to import workers, too.

Because if you're trying to use building materials that the local contractors are not familiar with, you're going to have a bad time.