Houses have been updated a bit, (see the new backyards!) as well as the generation improved slightly so there should be less broken ones. We’ve also got the basement placement algorithm working correctly, so lots of them will have basements now as well! It is still a point of potential improvement for the future though, and once we get z-levels in be assured that we will be rewriting virtually all aspects of building generation to take advantage of them.
It’s not really possible to take out house walls right now, but it has been discussed, we just haven’t gotten around to implementing something for it yet. 
For floor they already are constructible through the constructions (*) menu.