I will add a few comments and photos to the post.
For inspiration:
Words of the author "Mamont"
Let's start in order: if you make from the leatherette, then goes about 4 meters.
If from genuine leather, it is enough of one skins of 4.2-4.5 square meters. Thorough thickness - 6cm. The dimensions of wooden blanks are individual for the customer, but usually repel from the size of the seat 60x60cm. Here is a photo of blanks:
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