'''Method'''
Create a new virtual room type with a quantity of 3 in SETTINGS -> PROPERTIES-> ROOMS
Go to SETTINGS->PROPERTIES->ROOMS->SETUP and set the virtual room to have the same characteristics of your individual rooms but with a quantity of 3. Set:
*''Unit Allocation'': One per Booking
*''Overbooking Protection'': Property
Go to SETTINGS->PROPERTIES->ROOMS->DEPENDENCIES and use the following settingsfor the virtual room:
*''Requires Availability in'': Room 1 or Room 2 or Room 3
*''Assign Bookings to'': First Available Dependancy Room
*''Use Prices From'': Room 1 (to use the prices from room 1, alternatively you can use "This Room" and create individual rates for the virtual roomtype)