Q. How can I research Mies Van der Rohe's 50 ft Cube House

Step 1: Identify articles by searching Avery Index: [ mies van der rohe AND 50x50 ]

Keep in mind that the building will also be referred to as Fifty Foot by Fifty Foot.

Step 2: Search NYIT's journal locator and locate these journals.

Step 3: Search NYIT Library's catalog BearCat for books about the structure. If you fail to locate any broaden your search for books about the architect. In general terms, the Library of Congress location for Mies Van der Rohe is NA1088 .M65.

Step 4: Supplement your search using WorldCat. WorldCat will let you know if the topic has been addressed in the form of a book and where that book is located.

Tips:

• Library catalogs do not index books in great detail, meaning that it's a good idea to browse a physical book's table of contents and index.
• You can request articles and books online, or NYIT Library can issue you a Metro pass gaining you access to many libraries in New York City.

The project falls in the category of unbuilt prototypes. For your purpose, this citation appears to be the best: 

VLC Arquitectura, Oct. 2018, v.5, no.2, p.175-202, illustrations, plans, section details, sketches, photographs