Once you realize income you can write off expenses for the build. You defer expenses on your tax forms until you can write them off against income earned.

We have a large unfinished basement that is not used. We are thinking of converting to apartment at the suggestion of a family member who would like to rent it out.
Is the cost to have it finished with a bedroom, bath and kitchen something we can write-off?


Any tips on the best way to proceed? what happens if we do all the updating and our family member flakes out and then we can't rent it? How do we deal with any write-offs at this point?