Though I understand why the landscaping etc could not be done in winter I see no reason why the construction of the building - which seems to finally be enclosed (though not clad)- could not have proceeded. This really has been a terribly drawn-out project.
No part of physical construction can not be done in winter.
What is affected is curing time for concrete and in some cases a heated tent may be needed for pouring and/or curing.
But it can be done, albeit at a cost of some extra $
That, however, is a clear reason to prioritize that work for fall, so that you can continue w/carpentry/roofing and fit-out through the winter.
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By the way, landscaping in winter is excellent for the plants, provided the ground isn't frozen.
In Toronto it often doesn't freeze till Christmas and some years early January.
The obstacle to winter planting between November - January is typically that the nurseries have sold off or replanted any potted stock and shut-down for the year.
Sod is a bit tougher, because sod farms don't want to try and 'roll the carpet' once frost/freezing is kicking in; semi-solid ground can result in poor adherence, and may dry-out the sod some.