I created many of my building interiors by taking pictures of real buildings and industries. Its easier to get access to houses and retail, more difficult to get industry pictures. I used pictures from plants that I visited over the years, then resized and modified to give a nice industrial look through the windows. The detail is not that important, you just need enough for the illusion.
You can also build some interior "stuff", and with a light, it can look like there is a lot gong on inside.