price per buildable sq ft in Flatbush

I made a list of a handful of buildings in Flatbush that have recently sold and are slated for development, to determine the price per buildable sq ft. Basically I get an average of about $80/buildable sq ft. A developer might spend $100-300/sq ft to build, and then, if recent condo sales are a guide, the building is worth about $500-600 sq ft as either a rental or condos. He gets the difference in profit. The bigger the building, the generally lower price per build able sq ft. 

I'm assuming that developers themselves have made these types of lists in order to determine a fair price for a building project. 

Using this metric, one can also determine whether or not a building has a good chance of selling. being torn down, or being rehabilitated in some other way. For instance, 150 Lenox, currently for sale for $2.75m for 15,000 build able sq ft, is almost $190/buildable sq ft. It's overpriced. But perhaps a developer could add stories on top and bring his construction costs down. Or offer the seller less. According to even the highest priced sale here, it should be well under $2m. At a certain point it looks better to keep the building as is, or even to sell to an owner/occupier, perhaps at around $1.5m, about the prices of similar 3 story limestone buildings on Clarkson.