What does the design of the Roman villa have to do with the best leisure time for the owners?
The Roman Villa was designed around the leisure activities of the upper class. These activities included reading, writing, gardening, exercise etc.
In the first century BC, the picturesque Bay of Naples became a favorite retreat for vacationing emperors, senators, and other prominent Romans. (http://www.nga.gov/exhibitions/pompeiiinfo.shtm)
The villas of the richest Romans had private arenas, sport facilities and spas.
The design is around an open courtyard often filled with statuary of various sorts. The dining area would normally have been up on the second level looking down on the courtyard.
The villa was built to take advantage of the breezes and various changes in daily temperature to keep the inner structures comfortable to the inhabitants.
The Roman system of heating was ingenious as the floors were heated through a series of tile duct-works.
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Roman villas for the upper class were often built with the rooms facing an inner courtyard, often embellished with trees, flowers and even fountains. This gave people the privacy they wanted while at the same time being able to enjoy the outdoors. Another aspect was that this arrangement helped ventilate living quarters during the hot summertime. (Such architectural formats are still used today. For example, a replica in Florida of a such a patriarchal residence - Vizcaya - proves this theory out.)
Another adaptation was diverting a water source to come directly into the house. Such rudimentary but effective "plumbing" permitted the VIP of the epoch to enjoy the luxury of bathing at home (as opposed to the public baths of the time).
It seems that the Romans also took their meals in a semi-reclining position. Low couches and tables were used to this effect.