My boys live in a hutch in my shed year round. The shed itself offers wind and rain protection so I don’t have to worry about that, but keeping them warm enough takes work! Plenty of warm hIdes, loads of hay stuffed full in the hutch, plus I have four snugglesafe heat pads between my two boys (which are used day and night). I then have two blankets over their hutch, then a thermal hutch cover. I then pull a duvet over everything.
Having a thermometer is essential so you can keep an eye on the temperature they are being exposed to.
If your piggies are outside, then you will need to do all the above measures, plus ensuring the hutch is faced out of wind and rain.
If your piggies are new, young or have otherwise been kept inside, then you should not put them outside at all until spring time and when the night times are warmer. They need to be slowly acclimated to being out in winter and putting newly rehomed piggies (particularly youngsters) outside at this time of year is risky to their health.