Booking in Shared Calendars
The room booking functionality only works for appointments/meetings created in your personal calendar. The "Room booking" button of the Appointment window appears as disabled when an appointment/meeting is created in a shared calendar. This is due to a limitation of shared calendars.
If an appointment with room booking is required in a shared calendar, the best approach is to create a meeting request in your personal calendar and invite others that can add it to their own calendars.