If you have people outside your company that also need to reserve rooms in your office, you can share the room resource calendar with them by clicking on the down arrow beside the calendar you want to share and selecting the "Share this Calendar" option, but you need to have admin status to do this.
Under "Share with specific people" type in the emails of the people you want to add and give them the permissions to "Make changes AND manage to share."
You can choose to add only specific people from the mentioned groups and they can add others from their groups since they have the permission to share this calendar.
If you enable this, then people with whom you’ve shared your calendar can simply create a meeting and select the calendar they would like the meeting to be saved in. If they want the meeting to show up on their calendar as well, they need to invite themselves to that meeting to do that.