We got the sub-floor sheathing in place during the few non-raining days in December.
The first wall up on the second floor required the removal of part of the roof on the house ....
... so it was of primary importance to get the new roof on immediately.
With the existing house more-or-less protected, we could work on the other walls.
The rain was becoming a major annoyance, but we proceeded apace.
As much as I wished otherwise, because of the design, we had to start the the third floor before we could put a roof on the second.