All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If a house is prepared for rental, Zakah becomes due on its revenue, i.e. the rent money rather than on its value, once it amounts to the due Nisaab either by itself or by what is joined to it of other money or articles of merchandise, and a full lunar year has elapsed on it.
If the income of this year was spent on maintenance, no Zakah would be due on you concerning it this year.
Allaah Knows best.