As far as I understand it, we dont yet actually have a picture or a drawing of where Nat lived - everything posted or linked to so far is on the other side of the street, being numbers 1-6, not number 9 where Nat lived.
As 1-6 are four stories, and apparently built by the same 1700s developer (Mr Richmond) its possible they looked similar, and very likely at least the same amount of stories (4) as I doubt property was ever cheap in London and land could be wasted on low-rise accomodation. A 650 sq ft office is £1,500 (i think for a month) today (on a google search) - which compares well with Nats 2 shillings a week ( £0.10 or ten pence).
The Soho Hotel, on the site of number 7, is from £400 a night for a room.