This is a picture of the earliest discovered (231 AD) Christian home that was used for a meeting place. It was discovered in Syria and is called the Dura-Europos house church. The meeting area is on the left and the baptistery is on the right, toward the back.
I found this interesting quote from Spiro Kostof’s A History of Architecture:
“Indicative of a repressed and plebeian movement, the places of worship were exceedingly modest. Centers for the community were set up in remodeled, outwardly inconspicuous houses… To the first generations of believers the church was where the Christians were. The word ecclesia, “church,” signified the community of Christ that had no need for prescribed buildings to proclaim its faith and reaffirm its bonds. The people were the architecture. In the century or so before Constantine the random gathering places of this primitive Christianity slowly began to be formalized, and with the sudden breakthrough of the imperial conversion, the necessity of a monumental built order to project prestige and authority came to be recognized.”