Looking for alternatives to AutoCad to make floorplans and interior elevations for my kitchen
I personally use Google SketchUp to model both the interior and exterior of our house.  It may not have the depth of features you're looking for but if you're going for open source freeware that's pretty usable out of the gate you can't go wrong.  

As a side note, I have seen some people use Blender to do modeling, though more for in-home manufacturing.