This is an excellent question.  Since almost all channels sell room "types" rather than "individual rooms" we always recommend setting up Room Types in Myallocator, and then mapping those same Room Types to both your channels and your PMS.

If you need instructions on how to setup Rooms, please visit this article:  How To Setup Rooms

When you setup rooms in Myallocator, it is recommended that you create Room Types, rather than Individual Rooms.

In this Recommended example, you will see that I have two Standard Queen rooms in my hotel.  

Under the recommended setting, I create a Room "Type" called Standard Queen, and state that I have 2 of those rooms:

In this example that is Not Recommended, you will see that I have created individual rooms for each of the Queen Rooms and given them separate Labels (Standard Queen 1 and Standard Queen 2).

The reason for the recommended room types again is that the channels sell a "Standard Queen" room, and they do not specify which room (1 or 2) that is for sale.  Your PMS will insert the guest into the proper Queen room (1 or 2) based on which one is available.  In Myallocator, we work like the channels - we are only setting Availability, so we do not need to separate the rooms out from each other.