Federal Hall has a limestone roof also, tho they are not shingles. A bit heavier than that. I got to see them up close a week after 9/11 when they had a 1/2" of powdery dust and personal kind of office papers strewn about on them. RFP was for removing all the stuff. I asked questions about asbestos and was never called back.Book and Snake at Yale, has a marble roof. Each “shingle” ways between four and six hundred pounds. Other than making the building look like an overgrown jewelry box or as intended tomb, it does not make for the most practical roof. Excellent ballast, but makes replacement of the underlayments expensive.
Best,
Leland