Due to a lack of any outer walls, a profusion of windows and the flammability of the complex (most inner surfaces are wood, not stone, no sprinkler system), a sufficiently swift and chaotic attack against Whitman could be successful with a force significantly smaller than the population (500 students).
Primary points of weakness are the writing center (marked 1 in diagram) and loading dock (marked 4). Dense tree foliage in front of the center provides cover and camouflage. A downhill charge would swiftly bring forces through the writing center’s windows.
The approach towards the loading dock has little or no cover and thus should not be attacked until (a) defensive forces have been diverted to deal with the primary invading force or (b) until the Baker defensive wall is under attack (i.e., is burning). Once troops are inside, a quick thrust to the dining facility would eliminate any meaningful lines of defense.
At this point, Fisher would be the only structure left uncompromised, and the psychological harm from seeing all other buildings in fire and brimstone will make suing for peace quite easy. Terms should be highly advantageous for the invading army.