Sounds a bit like the base in Xcom or fallout shelter.
I would start with a big image as you thought and zoom in/out out using the 'layout scale' command from the system options. Anything you have placed will still have it's X and Y positions so it will stay where you place it.
The other element you need for this is an object for a 'camera' (just an invisible sprite with the scroll to behaviour attached to it). This way when you are zoomed in you can focus it to the particular room you want to see.
If you are a beginner, I highly suggest you start with Kyatrics list of FAQ. Study the examples and you'll pick it up in no time.