Before finding this tutorials, I thought that to model interiors people used 4 walls and connected them to make a room
I found these two tutorials made by Devin Olsen, which he takes full credit, I'm just sharing.
Here's the How to Model a 3d building and interior:
https://www.youtube.com/watch?v=uHNzPpXemR4
And Here's the How to texture a 3d building and interior:
https://www.youtube.com/watch?v=2DzZxp0R4vk
Hope you guys learn something with them, I sure did!
Good luck.