Initial vacancy-- how to classify expenses?

[Rivy S.]

When you first buy a property, and don't find a tenant until after the first couple mortgage payments are due, how do you pay for those expenses? Do you pay those out of your own cash, and consider those payments as part of your "all in"  number?  Or do you just classify those months as a negative return on investment? Do you pay them out of a general vacancy reserve pot? Or borrow against the future vacancy reserve of this property? 

This is mainly a bookkeeping question, I guess.  I'd like my spreadsheets to be reflective of the actual performance of each property, and I'm struggling with how to classify these types of expenses.