Work/Live Space Construction Costs Treatment

The entire property will be depreciated ... the workspace on your Sch C and the rental portion on the Sch E ... so keep accurate records of the cost to build ... if you can separate the costs fine if not prorate the total in some reasonable fashion like square footage. 

@Critter-3 is assuming that you will rent out the apartment, and you will live elsewhere. Is that correct? I thought that you are going to live in the apartment. We both think that the work space is for your own work. Please clarify the use of each part of the building. Are you going to rent out part or all of it, or are both parts for your own use?

If you will use the work space yourself, what exactly is "work"? Are you a W-2 employee or are you self-employed? Under the new tax law that was passed in 2017, if you are a W-2 employee you cannot deduct any business expenses for 2018 through 2025.