A guest's room is the guest room (the room you put guests in, duh!).
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
all of the guest rooms
one's own guest room
The guest room was large and had two beds.
Sure enough, rooms with ocean views are expensive.
At this hotel, all the rooms have concierge service.