Question

What is the most basic reason christians began to build church buildings, or have them built?

Answer 1

I don't know the logical answer for this, but my theory is that they built church building so that Christians would have a "safe" place. They could go into that building and know that they were safe from all of the world's drama, and they could focus on their relationship with God. 

Answer 2

Evangelist decided to spread the word of God and worship in larger groups so it was like a community of church families