Connect to Office 365:

Build a variable with all the rooms you want to include in the list:

$RoomAlias = Get-Mailbox -RecipientTypeDetails RoomMailbox -Filter {Name -like '*<name>*'} | select -ExpandProperty Alias

Create new DistributionGroup as a RoomList and add your rooms as members:

New-DistributionGroup -RoomList -Name '<name> Conference Rooms' -Members $RoomAlias