I want my money back from uncle Sam

[Walter Correia]

My wife and I currently own a owner occupied 3 family. We live in one of the smaller units, 2 bedroom 1 bath. We have a spare room that i use as an office sort of. Its where i write off my expenses. How do I know if i qualify for home office or how can i find a way to write off the space? We are also moving in the next month to a new home and the property will be rented out. Can we use a room in the new house as a home office?