First and foremost, we must remember that one traditional candidate for the site, known as the Cenacle, as it stands today, only reached its present form around the medieval period (there is still some debate as to exactly when), after experiencing numerous cycles of destruction and reconstruction. So, it's rather unlikely that Jesus and His disciples held their last meal in a wide, spacious Gothic room such as this - supposing that this is the actual site. The area would have looked totally different in the 1st century AD.
Many 1st-century houses in Roman Judea were small, box-like buildings, usually built from hand-made and sun-dried day bricks or stone. Interior walls (or also the exterior if one could afford it) were covered with a mixture of soil, chalk and straw or lime plaster. Wide benches of mud brick or stone for sitting and sleeping, and shelves for storage, were built into the structure itself.