I'll give you some advice from my own experience and more experienced people will certainly chime in here too-
If you plan to have 4 hens, don't start with 3. Adding a single new one to an existing flock of 3 will be more difficult than adding 2 or more. Keeping 4 chickens will almost certainly turn into a desire to keep 6, then 8, 12, etc......This is referred to as "chicken math" and it is REAL. I built my coop for 6, started with 3 and made it 7 months before I got 3 more. The next step is acreage. It can be very addictive.
Read, read, read, and read some more. Ask a lot of questions on the forums. The more you think about the the details (how will I collect eggs, how will I access the coop to clean it, etc) the better it will be. And you'll still want to change things when it is all said and done. I spent months pouring over the coop build pages on here and it was time well spent.
Assume that every night after you go to bed your coop will undergo a near constant attempt by critters wanting a free chicken dinner. Don't use chicken wire-use hardware cloth. Don't have any gaps larger than 1/4" to 1/2". Don't use simple latches-raccoons are smart little boogers.
Don't buy chicks until you have the coop well over 75% done. They grow so, so fast. You don't want to be up against a deadline with birds in your basement. Trust me
Read this article on ventilation. Even in Canada, I know this seems completely counterintuitive but it is really important. If you factor nothing else into your coop, factor this in. Also, consider chicken breeds that are known to be more appropriate in cold climates.
https://www.backyardchickens.com/a/...-go-out-there-and-cut-more-holes-in-your-coop
Most importantly, have fun! Chickens are great, I can't imagine my life without them.