Please note it is preferred for you to book the room by creating a meeting on your individual calendar and adding the room you would like to reserve in the meeting location.  This option will also allow you to use scheduling assistant in the meeting to show availability for the room.  Also, when doing it this way you will get a reply from the room either accepting or denying the meeting. 

Here are a few screenshots:

This one shows the room under location and the default setting here is for Busy.