These buildings were constructed on packed ground, they were more like huts actually. The hut was supported by a number of wooden pillars, a central and some 6 placed around it to allow the typical lozenge shape of these constructions. The walls were made of clay packed around a wooden skeleton structure. Spaces could be left in this for windows and door. The roof was made of straw, rather like a thatched roof in the UK country cottages. A hole was left at one end of the roof, towards the top so as to allow smoke to escape.
Given the organic nature of the building materials there is nothing left of these buildings except for the stump holes left into the solidified packed ground into which they stood.
The details which follow refer to the more advanced working methods which as I have already mentioned we can still see and visit. These usually date back to the imperial period although earlier remains still exist, such as the great drains (Cloaca Maxima) and the first walls of the city (the Servian walls).