how to deduct home office vs office?

Let me get this straight, if you have an office in your "home," you can only deduct the percentage you use for the office space, but if you "live" in your full-time office, then you can deduct the whole thing?

For example, if you have a 2-bedroom/1-bath house and you use 1 bedroom as a home office, you can deduct that space by the square foot for the office, but if you "live" in an office rental, can you deduct the whole office?