Hellenistic and Byzantine writers sometimes referred to the size of rooms by the number of dining couches that could fit into them. Do we know roughly what size of room this meant in modern units? Otherwise I'd guess that a five-couch hall was say 5 by 3 meters by visualizing 2 x 1 m couches around the perimeter packed as tightly as reasonably possible.
If you understand German than this nice website is very helpful because it deals with everything concerning living esp. the various types of couches and various types of triclinia:
http://www.antike-tischkultur.de/tricliniumstarts.html
If you click on the word "mehr" (which means "more") you will find a drawing how the couches were arranged and how the people fit on them. Unfortunately this nice website does not have an English translation.
Pardon me, Medusa, but I don't see a button "mehr" on that site.
Sorry, this site has not links to every page which I wasn't aware of. The "mehr" button will appear if you click on the chapters:
Einführung (Introduction) der Ausblick (the Outlook)
Lage im Haus (Plan of the House) die Illusion (the Illusion)
Ausstattung (Equipment) das Sommertriclinium (the Summer triclinium)