Hi!
We use wooden arks with an insulated corrugated iron roof, from Animal Arks. They're more expensive than some others, but they're warmer in winter and cooler in summer than many others. The arks made from recycled plastic are OK, and fairly well insulated. Many are lighter than the wood/iron arks: this makes them easier for you to move, but also easier for your pigs to move!
If you are keeping pigs all year round, I would advise you to use a floor. You can get away without one on really well-drained, sandy soil, but it makes their life a lot more comfortable, especially in winter. It also makes the arks less prone to being moved by pigs, or even by the wind: we've had heavy pig arks blown about by gusts before now!
All-wooden arks are also good, and if you are reasonable carpenters there are plenty of plans for building them available. They're well insulated, but you may need to put some metal edging on the doors to stop the pigs from eating them! Whatever sort you go for, a 6x8 foot ark or thereabouts should do for what you want.
If you're thinking about breeding pigs, a word of caution: you really do need a business plan before you start doing this as it's all too easy to end up with a load of pigs that you can't sell. You get peanuts for them at markets and it's heartbreaking to send your precious pigs off at a loss that way. Go on a pig-breeding course, or speak to some more established breeders in your area.
But yeah, keeping pigs is great! Hope you enjoy them when you get them