I have had reasonable to good results using JOSM with some of the plug-ins available, especially if you have access to the building you wish to indoor map or can get an old set of floor plans. If you want to take it a step further you can write your own .css style sheet and make the floors different colors so when you stack them with no filter to make stairs and inner walls line up, you can tell what floor you are working without having to constantly go back and forth to the filter.