The Villa dei Papiri was actually designed very true to the typical Roman-style villa. It contained key features that were fundamental to Roman architecture, such as:

an atrium: the entrance hall to the house; featured a impluvium, which was a small pool in the center of the atrium to catch rainwater that came in through the opening in the ceiling. (The Villa dei Papiri's lanuvium was surrounded by 11 statues of Satyrs pouring water).

a peristyle: columned porch that surrounded a garden (The Villa dei Papiri's peristyle had 10 columns on either side, and a large swimming pool in the center of the garden). 

These were key features of any Roman villa, and the Villa dei Papiri was a magnitude of these features. It was an extremely large and extravagant villa, which gives further support to the idea that it belonged to Piso. 


Note: Many of the pictures below are from the Getty Villa. This is because the Getty Villa was made to be a replica of the Villa dei Papiri. It is an almost exact replica of what it is thought the villa looked like.