Back in that time, there appears to have been buildings, as well as groups meeting in each others' houses, and down by the river etc
Of course there were buildings, Jesus was Jewish and taught in the temple (synagogue) as well as drive the moneylenders out of the temple because it was being used for commercial purposes.
The "house groups" you refer to, with the exception of the Last Supper, didn't start until after his death
The exception is of course his open air meetings, the Sermon on the amount etc, which were just that, public meetings, a bit like Speakers' Corner.
I sometimes think some Christian groups forget or ignore the fact that Jesus was a Jew of his day.