Only the marked walls and no ceiling over your head... I also thought we had built for dolls, but then I consciously realized (the logic, you know) that our basement is larger in qm than our current apartment, so not too small!
And that was the case. Wait until the ceiling is on, that will put the impression back into perspective. When only the interior walls stand and it is still open at the top, it always seems too small. The ceiling puts the proportions back into the right light.