Of the 50 most expensive home sales in the metro area last year, that’s the percentage of total spending attributable to just one building: the ultraluxe No. 9 Walton. The sale prices of the 19 units in the new Gold Coast building at 9 West Walton Street that made it into that upper echelon add up to $125 million. That includes 2018’s biggest sale, a 21st-floor unit that went for $12.1 million (a far cry, though, from the $58.8 million Citadel CEO Ken Griffin paid in 2017 for the top four floors of the building). While that purchaser has not been publicly revealed, other buyers at No. 9 Walton last year include the Cubs’ Jason Heyward, the Blackhawks’ Jonathan Toews, and Ferrara Candy Company CEO Todd Siwak, who paid $4.6 million for a 17th-floor unit — the 49th-priciest local home purchase of 2018. A sweet deal, indeed.