When setting up a meeting, click on the Scheduling Assistant tab at the top. Choose Add Rooms and pick the room you prefer to use and this view will show if it's open or not. This is also the easiest way to see other attendees' calendar availability for the meeting as well.
If you are someone who books a lot of meetings to a conference room, use this trick to see what is going on in that room:
Outlook > Calendar > Right-Click on Other Calendars > Add Calendar > From Room List... > Double-click on the calendar you want to add to Outlook.