The message
from Ian Stirling contains these words:

Why cast walls in stages, when you can cast walls in one?
Cast the slab for the floor.
Level it, get it nice and flat, then cast the other walls on it, and tip
them up into place.

Easy to do the damp-proofing, too. While the house is on its side, paint
one "wall" with rubbery masticy stuff then flip it over.

--
Skipweasel
Pay no attention to that man behind the curtain.