Oh forgot to say MrsDingDong
guinea pigs basically tolerate/feel comfortable at the same temps as ourselves .. so you can keep them outside if not an extremely cold winter as long as you put a big warm cover over their cage
(there are padded, thermal canvases available in pet shops for this purpose)
and of course they need plenty of warm hay to keep them cosy
However, they don't respond well to damp or cold drafts so you have to make sure the cage is well up off the ground and there are no cracks in it ...
I personally don't choose to do this though because you then have to clean them out (every four days or so) in the freezing cold!!! So I keep ours in our (marginally) warmer basement .... We also live in a town house and I don't want to attract vermin by keeping them outside (some of the feed inevitably gets pushed out of the cage or falls on the ground).
If you have a garden shed that would be good though as long as it isn't too dark ...
We always bring them upstairs for a bit of a stroke and a play and a run around most days too ..ours usually squeak when they need to pee so we don't have too many accidents to deal with ...
We are totally in love with ours ....and they have very distinct personalities ...can definitely recommend them as a good, easy, but responsive, all-round family pet ...
I would always buy two though so they don't get lonely, preferably sows rather than boars, as elderly boars have a tendency to get impacted "nethers" which means the owner then has to get involved in, er, un-decompacting them manually .... not pleasant before breakfast!!
Any other q's, don't hesitate ...g'night