First 
for guinea-pigs they're fab aren't they ?
My herd ( four sows and a neutered boar) have come inside for Winter nights now (they have a Pighouse shed so though they live out, its not out out - sounds a bit Micky Flannagan there)
In the interest of my sanity , and the try (ha!) to curtail their mess I made a C&C run in the small bedroom which is cooler. Ours live in a 3+2 so 2 areas of run.
They have tarpaulin on the floor under the run then a good layer of cardboard to protect their paws, puppy pads and paper. Would be newspaper but I have none so they've got pieces of Primark bag .
Then another puppy pad where they sleep and fleece on top.
They have they solid hay cookies rather than loose hay (they have loose hay in their boxes in the Pighouse)
Once they go out I'll roll up the paper/pads/fleece to chuck out (I used to wash fleece but TBH , I was sick of picking hay out of my machine and risk blocking it. And I've just had to replace my washing machine)
Sawdust and shavings are not recommended for guineas.
Sawdust is too dusty and shavings can harm their feet and fur.
Megazorb is recommended.
I use Ecobale in summer (chopped card equine bedding) so they don't overheat.
Hay in winter on top of soft pet straw to insulate.
Some cat litter wood pellets are rodent safe (we use one from the Range in a yellow bag which is rodent safe)
And piggie pooh is very inoffensive compared to hedgehog, but they pee rivers . Especially sows.
Are you thinking of boars or sows (or a neutered boar+sow mix?)
Are you looking at Rescue? There will be loads out there but you'd likely have to wait till after Christmas.