You can use Avery Index to search architecture magazines specifically for articles that include plans, drawings, elevations, axonometric drawings, sketches, maps, etc. Then requests scans of the articles using the Find it at CU button and requesting from Interlibrary Loan. Use the Document Feature check boxes in the advanced search to limit to articles with specific types of illustrations:
If you are looking for plans of a specific building there may be no book about that building in particular. However, it is probably in books about the architect in general, so it will be best to search for the architect. You may have to go to the call number section where all the books on that architect will be and look through different books to find plans of sufficient detail.