My question was: Is it sufficient that it looks like an office?
IRS clearly states that in order to qualify for a home office, it needs to meet two requirements:
1. Exclusively used for Business
2. Regularly used for Business.
The key words are "exclusive" and "regular". However they are still vague and I don't believe that it means that other family member can not even enter the office.
What is a acceptable set up for home office?