The topic of winter housing comes up time to time. We've used a variety of temporary structures and open sheds for years. Finally this past winter we build a large hoop structure 38'x96' which is up on cedar posts to keep it above pig reach.
It's great - Wish I had done it seven years ago like I planned...
For us it is a winter structure primarily and it has already paid for itself by letting us farrow more through the deep cold season. In other climates the summer shade could also be very valuable.