The University Archives holds a wealth of material documenting the construction and layout of campus and buildings since 1903.
Helpful places to start:
Many maps of Cal Poly are digitized and browsable at the Online Archive
Here are selected representative maps found at the links above, in chronological order:
Additional maps of interest:
Note: If you are looking for a specific year that you do not find at the links above, you can also often find maps of campus in the course catalogs.
Image caption: 1999 campus map from the 1999 Course Catalog, pg 529. https://digitalcommons.calpoly.edu/catalogs/85/
Many aerial photographs of Cal Poly are digitized and available on the Kennedy Library Online Archives.
Image caption: Aerial view of Cal Poly, looking north, circa 1940. https://digital.lib.calpoly.edu/ua-pho00000194
You can access many of the original architectural plans for campus buildings via the Facilities Web Plan Room: https://afd.calpoly.edu/facilities/campus-maps/web-plan-room (Cal Poly login required).
For projects that are not found at the above link (such as demolished buildings), University Archives may have the original print drawings.