There are a number of ways and it depends on the design of your database.
Assuming that you have one field, rooms in each record, you can pull up a found set of records and sort them by the Rooms field. Then a summary field defined as the "count of rooms (or any other never empty field in your table)" can be placed in a sub summary layout part "when sorted by Rooms" and you'll get a count for how many records have Twin, how many of Triple and so forth.
There are also ways to set up a relationship so that records with "Twin" are the records that are linked via relationship to the current record. And then there are several ways to use either a summary field or the count function to count the number of related records.