Just to add.....
..... I haven't found out yet how to get the foundation under the house. I can get it to spawn above the house..... and yes.... I did say... "above". But I can't seem to get it under the house yet.
I may have to build a second house beside the one i'm building just to get the first floor on a foundation, then move my house over to the foundation. I'm not even sure if that'll work, and to be honest. I'm a little afraid to move the house again, because the last time I did that I lost walls, furniture, and of course, just for fun, the platforms decided to reshape themselves to different heights from what I had them set at.
It might be faster to simply build the house again from scratch making sure first I have the foundation setup before continuing.
(And i'm using the words "faster", and "simply" with a bit of sarcasm.)