I’m looking for advice on how I can help a feral cat survive the upcoming winter

Over the past couple of years, our house seems to have become “the” place to go for many of the local abandoned or feral cats. Some have just dropped by to beg a meal or two before moving on, and others have hung around and “guarded” our front yard for us—for food, of course. Our family has taken in three of these cats so far: one was a half-inside/half-outside cat who ended up being injured in a driveway accident and is presumed dead, the other two were a pair of tiny, tiny kittens that had been abandoned and now full-time inside cats—they’re now the size small pickup trucks!

About two months ago, a very sweet two-thirds grown tabby cat—female, I’m guessing—showed up and took up residence in our front yard. Despite my best efforts to befriend it, the tabby rarely lets me close enough to touch its back—barely—and then only a second at best. The cat does show interest in what might be going on inside our house—especially regarding our two inside cats who watch it intensely—but it won’t get close enough to an  open door to take the next step and come inside. Since the tabby shows so much fear/skittishness towards people and apprehension about coming indoors, I’m calling the cat, “feral.”

The tabby eating in our driveway. Note its left ear: Is this perhaps "tipping?" A sign the cat's been neutered?

We live in urban Kansas and our winters are cold. Snow, ice, and a lot of cold wind is the norm here, so naturally I’m very concerned about how the cat is going to survive this coming winter. I’m fine with feeding it, but even if it was interested in coming inside, I really don’t think our tiny—and I mean, tiny—house can hold another cat. I have no problem “building” a shelter for the cat, but my time is limited and I want to get whatever I build “right” the first time—I want the cat to use it, and for it to do the intended job: providing a warm shelter.

I’ve seen various plans online for building winter shelters that appear low-cost and fairly easy to make. Below is an example from urbancatleague.org.

Well, without going on and on, my questions are these: Has anyone out there had any success with such a shelter? Do feral cats actually use them? Does anyone have any tips or suggestions for me regarding helping this cat survive a Midwest winter? Please advise!