Your guinea pig will be comfortable in the same temperatures that humans are generally comfortable in. If this means that you have to bring your guinea pig hutch inside to an outbuilding in the winter then so be. They must have plenty of bedding in their hutches with the sleeping compartment full to the top of the hutch (if kept outside) so they can nestle and be warm.
They are unable to stand getting damp and cold as this can bring on pneumonia quickly so regular cleaning of your guinea pig hutch in the winter is even more important. For this reason it is sensible to site your guniea pig hutch facing away from prevailing wind so the rain does not get blown it to the cage.
Cavies do not like very cold weather or excessive heat in the summer as both can be potential killers. Please bare these things in mind when choosing where to site your guinea pigs hutch.