Hmmm, so many things to consider... Most have already stated good ideas and a lot of the peeps who have replied also have coop pages where you can see what they've built in their own state and with the chickens they have.
You don't mention (or I don't remember seeing) what breed of chicken you are ultimately looking to have OR for what purpose (when you mention D'Uclles, I'm thinking you want a pretty, possibly mixed, flock w/o regard to regular egg laying). Many breeds have different requirements based on size and type and there are specific breeds that do well or were specifically bred in Canada and are considered dual purpose birds (and can be VERY friendly, too).
I agree the TSC coop is too small for LF breeds. Their durability in your weather patterns is questionable. I'm surprised they even market them in your area, maybe I'm not understanding weather patterns N of the Great Lakes. Snow until MAY??? 3' of snow right now where you are looking at building? I'm figuring it is also a very wet, heavy snow, but could be wrong...
Even an 8x4 coop is too small for 2 LF birds in that type of weather - like others - ask me how I know. After 8 straight days of alternating heavy rains w/ drizzling mists and lots of wind every day, my 2 - 4x8' coops are pretty nasty and I have a very unhappy
pair of Ameraucana in one and a
trio of Ameraucana in the other. Ameraucana are not very big LF birds - and they aren't full grown yet. Even when I set up some small, temporary, covered pens for them to venture out in while I was around to observe - they did not. The wire covered runs aren't even started yet. I started with a quad of Bielefelders in each of these coops just 4 months ago - once they got bigger - they are too large for this size coop but 8 will fit on the roost...
As to chicks or pullets? Again different requirements... I LOVE chicks. I also LOVE eggs. I ultimately started with chicks BEFORE I even had any type of coop (Y did they need one?) since I was given 15 CUTE bantams of unknown sex or breed at Christmas 2010... They and LF production type, hatchery purchased birds "survived" our learning - while free ranging and nesting/cooping in our very large tin covered barn. It was almost 3 full years before I found BYC and learned I had done a lot of things "wrong" - yet we had lots of eggs to eat and chicken in the freezer (mostly bantam cockerels). Built our first CP hoop coop/tractor in 2014 and we go on from there...
Here on our new and much larger property - we have different predators at different times of the year. While having a lot more open space - chickens usually die here when free ranging (& sometimes in uncovered runs) - especially between 1 December & 1 March - when larger animals are HUNGRY (even domestic dogs that are allowed to run loose - their collar tags point out that they came from miles away).
In 2018, I have gotten many different breeds from breeders instead of through hatcheries from TSC and the feed store that brings in chicks. Some as 3 day old chicks, some as "started birds" (both cockerels & pullets) & some fully mature breeding birds. I am still discovering which breeds I like - I know I was surprised that some of my birds didn't even start laying until they were 9-11 months old (I purchased those as "started" birds at 3 months of age - 55 Flowery Hens, Cream Legbars & Rhodebars. The first set of 11- 55 Flowery Hen incubated eggs were all fertile, but none made it to hatch). I found other birds (buff & lavender Orpingtons) that I was recommended to purchase and that are supposed to be great dual purpose birds for farms & homesteads to be unthrifty (for us - you sneezed in the brooder area and they'd keel over dead!), not very big when processed (lots of pretty, fluffy, lavender and buff feathers, though) BUT do live up to their name as VERY friendly birds - even the mature rooster. W/O predator loss, I had the most loss from that breed of birds w/ unrelated bloodlines from 2 breeders. Of 20 birds purchased over a 4 month period, the ones I'm left with today are all related lavenders, none of the buffs - a mature rooster & 1 (of 4) mature hens I purchased him with, 1 cockerel he sired & 2 pullets he sired. The two pullets are both laying - but not consistently yet. One hatched in April and 1 in June. The last mature hen was laying and is now back to not. She is the oldest and will be 3 yrs old this summer. She molted last fall.
While you wait to build - you can purchase items on sale, gather free items & take them apart (pallets, partial sheds, ??) in preparation for building or purchase supplies you may need just so you aren't having to pay for everything all at once and even build your own feeders and waters, so you spend less money on those, too. I personally LOVE Cattle Panels (CP) and we found that they do work in the snow and wind of MT (& Blooie, a member here, had hers in WY) as well as here in NC in the rain, sand and humidity. Many different styles to make with them, too. Our next one will be made using old tires as the base to raise the panels to accommodate DLM. Hopefully, I will start that one soon, but I have to start/finish the run between the 2 - 4x8 hoop coops, first. In the pic below, you can see the two 4x8 coops from our front porch (two blue tarps are the roofs w/ the big pine tree almost centered between the two) and a couple close ups showing with birds in them... I don't have pics of the Ameraucana in either of them yet - just the Bielefelders. The outsides of the pallets all now have wire attached and the bottle walls have been replaced by wire.
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& pics before the DLM bedding & chickens put in them
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O, and I am a true novel writer in forums!!