In that situation, March makes more sense for the reasons you mentioned plus weather. Framing in winter is much more difficult---meaning the possibilities of more trouble and mistakes.

And, rain has a less long lasting impact than snow as a rule.

Another point is dust/construction debris. Being able to open windows is a huge plus.

And, holiday off time is minimized.

How tight is your budget? The longer into the future you go, the harder it is for your builder or any of his subs to know what their materials costs will be. And sorry to say but companies come and go. The builder right now can probably get firm pricing to begin in Sept. But not in March. The raw materials market is very volatile, with copper and wood costs, as well as freight surcharges. There is know way of knowing, of course. But you do expose your project to higher cost risk the longer out into the future you push it.

Thanks. we originally bid the drawings to 4 builders. Down to 2 with extensive references and solid portfolios of home additions, remodels. Both were not phased by the time of year to do the construction. They said its HO preference. I imagine that these guys are interested in making money all year round of course. If we start in September here in the northeast we are told it should be airtight in 3-4 weeks. Meaning by mid to late Oct. The rest of the work is the interior remodel from new floors throughout, kitchen, HVAC, etc.

Much of the issue is our tolerance to the indoor commotion for however long it takes. As much as we wish to get it done sooner than later, we know that once we start it's both feet in. No pause or reset buttons.

The contractors both acknowledged that it would not be easy once they bang through the house.