Hint #1 says that the letter Z is missing, therefore we have 25 letters. Both nominators and denominators range from 1 to 5, which makes 25 unique combinations. That's suspicious - let's try a 5x5 box filled with letters A-Y (standard right-down order). Now nominators/denominators code columns/rows and we can directly read out:

B FOUR THREE
C SEVEN FIVE
C ONE TWO
A ONE FIVE
N E CORNERS
X IS THE SPOT

Looking in the campus plan, finding the corners of the buildings and constructing the center of the quadrilateral brings us to the roof of B 22.