3D Builder is Saying "One or more objects is invalidly defined"
How thick are those walls? 3D printers cannot print zero-width surfaces (and slicers cannot slice them). 3D Builder has tried to make your model printable, but obviously not in the way that you might have hoped for. You need to go back to Sketchup (or some other CAD package) and give the walls a definite thickness (and one big enough for a 3D printer to handle).