Be able to import an image to be used as a guide to build your own maps

Would be great to be able to import 2d maps that exist already to use them as a guide to build on them your own maps. You should be able to control the opacity and size to make it fit when you build your own maps.
Another possibility would be being able to put it under the ground floor and have a button to make the ground disappear so you can check if you are following the map or not.