He found that apartments in 99-unit projects — which presumably will all use 485x — are 200 square feet larger, on average, than in comparable non-485x projects. In a building where the annual rent per square foot is $85, an extra 200 square feet would raise the monthly cost a lot. For example, Unit 9E at 150 Fourth Avenue in Brooklyn, the decade-old Intrata Park Slope, is 1,000 square feet and available for $7,400 a month, or $88 annually per square foot. At 1,200 square feet and the same price per square foot, the rent would be $8,880. But still, Unit 9E with an extra 200 square feet could mean an extra bedroom and $1,400 more in rent.