Rhetorical question?
Various methods can be used, number and colours for each side (aspect) of the building.
As you look at the building, Front is White aspect, Rear is Black aspect (think back), Right is Red aspect, and Left is Green aspect. So when inside the building looking out to the front, red is on the left and green is on the right (same as port and starboard).
Alternately Front is 1, Left is 2, Rear is 3 and Right is 4.
Key thing is that all the team know which side is designated the front, and can count and know their left from right.