The Flatiron Building was designed by Chicago's Daniel Burnham as a vertical Renaissance palazzo with Beaux-Arts styling. Unlike New York's early skyscrapers, which took the form of towers arising from a lower, blockier mass, such as the contemporary Singer Building (1902–1908), the Flatiron Building epitomizes the Chicago school conception: like a classical Greek column, its facade – limestone at the bottom changing to glazed terra-cotta from the Atlantic Terra Cotta Company in Tottenville, Staten Island as the floors rise – is divided into a base, shaft and capital.

The Flatiron Building has become an icon representative of New York City, but the critical response to it at the time was not completely positive, and what praise it garnered was often for the cleverness of the engineering involved. Montgomery Schuyler, editor of Architectural Record said that its "awkwardness [is] entirely undisguised, and without even an attempt to disguise them, if they have not even been aggravated by the treatment. ... The treatment of the tip is an additional and it seems wanton aggravation of the inherent awkwardness of the situation."

He praised the surface of the building, and the detailing of the terra-cotta work, but criticized the practicality of the large number of windows in the building: "[The tenant] can, perhaps, find wall space within for one roll top desk without overlapping the windows, with light close in front of him and close behind him and close on one side of him. But suppose he needed a bookcase? Undoubtedly he has a highly eligible place from which to view processions. But for the transaction of business?"

When construction on the building began, locals took an immediate interest, placing bets on how far the debris would spread when the wind knocked it down. This presumed susceptibility to damage had also given it the nickname Burnham's Folly. But thanks to the steel bracing designed by engineer Corydon Purdy, which enabled the building to withstand four times the amount of windforce it could be expected to ever feel, there was no possibility that the wind would knock over the Flatiron Building.

Nevertheless, the wind was a factor in the public attention the building received. With Broadway on one side, Fifth Avenue on the other, and the open expanse of Madison Square and the park in front of it, the wind currents around the building could be treacherous. Wind from the north would split around the building, downdrafts from above and updrafts from the valuted area under the street would combine to make the wind unpredictable. This is gave rise to the phrase "23 skidoo", from what policemen would shout at men who tried to get glimpses of women's dresses being blown up by the winds swirling around the building due to the strong downdrafts.