Here at Drift Oak Ranch, we believe in using what works. We have many types of shelters, from commerical pig huts to lean-to's made from extra materials we had left over from other projects, even some with pallets. As long as you can provide an area where your pig can get away from the elements, a lot of things will work.
The Idaho Pasture Pig Facebook Page has so many examples of shelters, including some nice plans for A-Frames, the breed owner's preferred shelter. We actually have only had one A-Frame here and our pigs didn't use it. We love the commercial pig huts and they are great for farrowing, but they are expensive. Using old sheet metal from a buiding project, Philp designed a "hut style" shelter that is not only less expensive, but it works well for us as we can open up the back to facilitate air flow and we can cover it up during the winter. I also like the lean-to style since I like to sit with my mama pigs while they farrow, and that way, I have lots of space. We keep the back of the lean-to off the ground, so it provides a lot of the same protection for piglets so if mom lays down, they can escape. This is the logic for A-Frames as well. Mom can't accidentally squish her piglets when she lays down.