Hard core geojson
There are online geojson editors, such geojson.io. You can find your building, map it, add properties such rooms name, then save it as geojson or as topojson file.

Note that geojson.io doesn't allow an infinite zoom, so your drawing may be quite approximative.
In your D3js code, you will have to autofocus on your json data (shape). A convenient working example is explain in the 2nd half of this answer, the D3js call
and Focus
sections.
Witty SVG
Designing your building as an SVG / XML file using Inkscape or some other vector editor would be a bit longer to do, but will end up into better end results. You then use d3.xml(http://yourwebsite.org/file.xml, function(data){ ... })
. I have, unfortunately, too few expertise in this direction, but it's the way I would go for if quality is requested at that level.