Roman Mosaic found in Tuscany

[Nathan Ross]

resources online giving the floor plans of 4th century villas?

If you're looking for villas, rather than the big urban domus (many of which, in the fourth century, became as massive as rural villas, and often more elaborate!), then there are plenty of examples to look at.

Try doing a google image search on any of the following late Roman sites and you should find plans and web pages:

Villa Montmaurin, France
Villa Olmeda, Spain
Villa Romana, Piazza Armerina, Sicily
Villa Quintilii, Italy
Villa Echternach, Germany
Villa Nennig, Germany
Villa / Palace Konz, Germany
Villa Seviac, France
Butrint Triconch Palace, Albania

You might like to scan through the online portions of this book too (the paper version is quite pricey, unless you can get it through a university library):

Housing in Late Antiquity

That should give you some starting points. If you want to look at some more urban dwellings, this site about Ostia is excellent - most of the surviving buildings are Hadrianic/Severan, but some have later additions (go to 'clickable plans' in the left panel, then click on the highlighted individual buildings in each Regio map):

Ostia Antica

*Edit* - this book also has a lot of plans and descriptions of later villas - and some of the chapters are in English. Well worth a scan through:

Villas Tardoantiguas en el Mediterráneo Occidental