So they hurried off and found Mary and Joseph, and the baby, who was lying in the manger. Luke 2:16

People didn't have barns or stables in first century Nazareth.  You had a house, with a couple generations jammed inside, some animals that roamed around - sheep, goats - and a little land to plant food.

We believe Jesus was born in an area where animals were kept because of the presence of a manger at his birth in Luke 2.  A manger is a feeding trough that grain and food was thrown into and the animals ate out of it.  Since it was the only piece of furniture available, Jesus slept inside of it.

Since there was no room for them in the "inn" (aka the guest rooms), the family probably put them in a basement or storage room (aka garage) or a shelter for animals.  Some believe it was a cave which may be possible.  However, people kept their animals within the confines of their homes for protection from thieves.  Most carpenters didn't have flocks of animals, only a few.  It was expensive to feed them, so you could put 4-5 sheep/goats in a storage room with some hay.

That's probably where Mary and Joseph slept and then gave birth to Jesus.