Strategies for space planning may include:

Stack common-use areas so that all janitors’ closets are located in the same place on each floor, then run a single exhaust duct vertically through the building for each exhaust fan to tie into.    
Add height to the deck-to-deck elevation to provide extra space above finished ceilings for ductwork.
Locate rooms identified as containing hazardous material adjacent to outside walls to reduce the need for more ductwork.