You are correct. Interest paid during construction must be added to the cost basis of the property, and interest incurred before and after construction can be expensed. The construction period ends when all production activities reasonably
expected to be done are completed and the property is placed in
service—that is, made available for rent. Once that occurs, you can deduct your interest and other expenses. As for the property tax paid in 2018, you can either deduct it as an itemized deduction (may be limited due to SALT deduction limit) or added to your cost basis.
