As you work through your Schedule C, you should indicate that you have a home office. TurboTax will take you through a series of questions to be sure that you qualify for the home office deduction.
If you do qualify, then there will be a question asking how much of your work is performed in the home office versus other locations. The answer to this question will be used to calculate any income-related limitations for claiming the home office. Be aware that the limitation may prevent you from claiming both the home office and another office location.
As for claiming the regular office in a building, you would simply enter the expenses related to this office as a business expense on your Schedule C. For example, if you pay rent to use that office space, then enter the rent amount as a business expense. There are no special qualifications to meet to claim an office that is not part of your home.
You can't claim a home office deduction unless it is your regular place of business. If you also maintain an outside office, then it will be very difficult to qualify for the home office deduction even if you do some work there.
https://www.irs.gov/taxtopics/tc509
Technically the rules say this
A portion of your home may qualify as your principal place of business if you use it for the administrative or management activities of your trade or business and have no other fixed location where you conduct substantial administrative or management activities for that trade or business.
You can have more than one business location, including your home, for a single trade or business. To qualify to deduct the expenses for the business use of your home under the principal place of business test, your home must be your principal place of business for that trade or business. To determine whether your home is your principal place of business, you must consider:
The relative importance of the activities performed at each place where you conduct business, and
The amount of time spent at each place where you conduct business.
Your home office will qualify as your principal place of business if you meet the following requirements.
You use it exclusively and regularly for administrative or management activities of your trade or business.
You have no other fixed location where you conduct substantial administrative or management activities of your trade or business.
It's going to depend on the facts of your situation, and what duties and tasks you perform at home compared to your office.