Some bhikkhus take a daily alms-round as a special practice (dhuta nga or tudong) and will normally always want to go.
Many other monks will be happy to receive food brought to them.
Please ask or observe how the monk practises. There is no harm in offering to bring the food, for if the monk prefers to walk on an alms-round he can explain about that.
Learn more about the Theravadin Buddhist Monk’s Rules here: