Mosaics, which were used for the floors, bear some similarity to road construction in that they were layered and set atop gravel. On top of the gravel was a layer of mortar and on top of that the tesserae (colored cubes of marble, stone, or glass) were set either on their own or glued onto a piece of linen that would be soaked out later.
See Jane Fawcett's Historic Floors for more on the construction.
