Reddit mentions of The Architecture of Warren & Wetmore

/u/Vitruvious gave many great links. The books in that link to the Classicist bookshop are excellent, but one on that list I've found exceptional is 'The Study of Architectural Design' by Harbeson. its a collection of essays he wrote in Pencil Points magazine that outlines many of the methods of the Ecole des Beaux Arts. I found it incredibly helpful in understanding classical design at the beginning of my career.

You might also look at some of these books on early 20th century American architects by Walker/Pennoyer. They are filled lots of plans and drawings worth studying about prominent NYC architects of that time:

The Architecture of Delano and Aldrich

The Architecture of Warren and Wetmore

The Architecture of Cross and Cross

Another prominent apartment architect in NYC was Rosario Candela. there is a monograph out, but I haven't looked through it yet.

For buildings in Paris, you can look at Krafft & Ransonnette - 'Maisons de Paris. There was a reprint in 1992 that is good if you can find it used.

If money were no object, 'Motifs Historiques d'Architecture et de Sculpture d'Ornement' by Cesar Daly is excellent for interior elevations of superb French interiors. Unfortunately, I haven't found a reprint.

For contemporary classical apartments, look at some of the more well-established NYC classicists. Some of their monographs and even their websites include plans. Let me know if you need any recommendations on firms.

Hope this is helpful, and feel free to ask questions!

EDIT: Found some of the Cesar Daly books online:
Volume 1
Volume 2

He also published L' architecture privée au XIXe siècle: nouvelles maisons de Paris et de ses environs (Sér. 1,2): Maisons à loyer and has some good plans.