Ferret, I don't want to be a downer since I don't know what part of MI you're in, but I will tell you that here in central MN, an open sided coop WILL NOT WORK. It's just too cold. My 6x8 (4 chickens) coop is fully insulated, walls and ceiling, with large southern windows for sun heat, and even with 24/7 (ceramic bulb) heat my coop holds at around 15F throughout the winter. If I had an open wall, I'd have dead chickens. I know that the book talks about being in Canada, but you really need to do some more research before committing to this design. There is a lot of information on this site with lots of people's opinions - I recommend using the search function in the blue bar up above and reading everything you can get your hands on. I know that Patandchickens did a very thorough review of the book as well.
And I don't have silkies, so I can't say from experience, but I didn't think they were particularly cold hardy. My chickens are, plus they are big and fat but they hate the snow. So they spend most of the winter indoors (ETA: inside their coop, that is).
Again, sorry to be the downer. Just come at it with both eyes fully open.