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 here: Maps collection
Here are some of the above maps, listed in chronological order:
There are also digitized maps via Facilities: https://afd.calpoly.edu/facilities/campus-maps/maps/historical-visitor-maps/
Many aerial photographs of Cal Poly are digitized and available on the Kennedy Library Online Archives page.
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 listed at the above link, University Archives may have the original print drawings.