There was, in the Nineteenth Century, a considerable amount of tension between architects and librarians as to the proper design for a library. Librarians, without actually articulating it in precisely this fashion, foreshadowed Louis Sullivan's famous architectural dictum: Form Follows Function . Architects, in general, don't always seem to get this simple statement, and even in this century there are any number of beautifully formed, largely dysfunctional, libraries across the land. Kenneth Breisch (cited on the opening page), and Abby Van Slyke, Free to All: Carnegie Libraries & American Culture, 1890-1920 (Chicago University Press, 1995) both discuss the issues, and it is not my intention to get too deeply into the arguments.
As the librarian son of an architect I obviously have mixed feelings on the topic. In general I have to side with librarians who want a large degree of functionality in a building. On the other hand I have come to recognize the "public icon" aspect of library buildings and would argue that libraries do not, indeed probably should not , be functional to the point of being boring, or worse yet, ugly. The most functional library in which I have ever worked is not, truth be told, a thing of great beauty. But I digress.
Part of the Report is devoted to a chapter by Justin Winsor on "Library Buildings" (465-475.) And part of that chapter is devoted to Winsor's "Plans for a Library of One Million Volumes' (sic) Capacity" (472-475.) The plans, reproduced here, were worked up by Winsor and the Boston architectural firm of Sturgis and Brigham.
The main part of the chapter is devoted to some very practical, and very detailed advice on library buildings. Winsor reaches the level of describing how bookends should be made, and then describes a book location scheme involving case, range, shelf and book number. The example he comes up with is 3825.5, meaning the 5th book of the 5th shelf, of the 2nd range, of the 38th case. Quite clearly Mr. Winsor had not met Mr. Dewey at this stage of his career.

Winsor starts his description of the building thusly:
The main Book Room, marked A, is to have seven stories, with glass floors between and a glass roof, each story 8 feet in the clear; the walls to be shelved; the cases double faced, to stand on each floor in rows, with passage 2 feet 10 inches between....
This was intended as a closed-stack library. In fact the description quoted here sounds a great deal like the later "central book tower" concept without the stacks functioning as part of the structure. One can only hope that Winsor intended opaque glass floors. Perhaps not, as earlier in the chapter he mentions the necessity for bathrooms for each sex "if women are also employed on the staff."
Winsor continues:
The section for Popular Books, B, is to be similarly arranged, but of only two stories, while the five stories above B, extend over the Popular Delivery Room as shown in K, (second floor plan, below) and so connect also with the room A on each story, forming a component part of the same.
The small room on the NW side (I am assuming North to be the top of the illustration) is a "student's room" intended to house what we would now call study carrells so that small collections of books could be maintained there on a protracted basis.
Winsor's design, and commentary, make plain the continued division along class lines visible in BPL.
A side entrance is arranged for such as visit the library for popular books only, and the noise attending the larger concourse of such readers is kept apart from the greater quiet of the the more studious frequenters of the General Delivery Room.
In one sense Winsor's "popular" section is the equivalent of the browsing collection visible at the bottom of the main floor plan of the Northern Iowa library linked above. Given that Winsor is implicitly describing a public library the relative difference in square footage is unsurprising.
Click on the small image for a full-sized version.
As we move up the building, Winsor's description is a little less clear. "Contingent" spaces start occupying more square footage on the plan, and in the text. While he is quite clear about the multi-story nature and usage of the book rooms (L and K) it is not at all clear how many stories are involved on the east side of the plans- or for that matter on the south reading room. An elevation of the building would have been very nice.
Click here for the basement plans.
Looking at the Winsor plans, and the Northern Iowa plans linked above is instructive. The basic layout at Northern Iowa is much the same as when I got there in 1974. Conceptually the building goes back to the 1960s. Given the almost hundred year difference in architectural and library practice, particularly the development of open stacks, I think we can make a case that Winsor did well. The basic rectangular layout, the proximity of service points and reading areas, and the separation of various functional areas, are all echoed in the later building. Winsor even has elevators in his design. Look very carefully to the left and right of roughly the middle of the main book stack (A) and they are present.
Any further commentary I think I will leave to the architecturally inclined among us.