*A solution would be to add a selection field (meeting room) on the calendar.event form view.
*Then you could create a new menu that will be related to calendar.event and in this new menu/view you could do an edit action and add a domain for the new custom selection field that you have created for the meeting rooms (custom field is different than false).
* Then in order to make the distinction between the meeting rooms clearer you could define a specific color by meeting room and in order to do that you will have to edit the calendar view and change the color:

<?xml version="1.0"?>
<calendar string="Meetings" date_start="start" date_stop="stop" date_delay="duration" all_day="allday" readonly_form_view_id="691" event_open_popup="true" event_limit="3" color="technical_name_of_your_custom_field">
               <field name="name"/>
               <field name="partner_ids" write_model="calendar.contacts" write_field="partner_id" avatar_field="image_small"/>
               <field name="is_highlighted" invisible="1"/>
           </calendar>