So does your boss own the building? Consider your location carefully as you may be required to make it ADA accessible (if you get a permit). If you don't make it ADA accessible, your boss might run into problems if he ever hires a handicapped person, or he might have to upgrade it to comply (leave extra room).

We put in a shower in our office and were required to make it ADA accessible and it doubled the amount of space needed. We used one of those prefab all-in-one situations. Don't forget the fan.