The Guardian did a nice job of collecting construction photos of various buildings here. One comment: the fifth photo, labelled “The structural framework of the central building of the New York Public Library, 1905” is clearly the structure for the stacks, since the columns are too small and too close together to be any area in that building meant for regular human occupancy.
Here’s another, from 1904 or so:
That’s the construction of concrete stairs in the 23rd Street Station on the original IRT line (now 23rd Street on the Lexington Avenue line), between the platform to the right and the entry to the left. Note the very large area of vault light above, allowing daylight into the below-ground station.