As I understood since the place is commercial building and owner is shareholder employee should have Sch E on his individual tax return.

I searched for the home office expenses, at this case: The S corporation can pay you for the costs of a home office under an "accountable" plan for employee business expense reimbursement and do not need to file Sch E, and but should consider Sch A to be prorated for real estate tax and Mortgage interest.

If it is, hard to find mortgage interest monthly since every month the rent expense should be reimbursed. How to find it?

Am I right? please correct me, thanks.