Hello Noctus
Welcome to the world of guinea-pigs if you are planning to join us Pig Slaves 
I have 3 at the moment, I've gone between 2 and 5 , at the moment I have 2 sows who don't want to co-habit with our neutered boar.
We have a Playhouse (its roughly 6'6" square) so we have two divided areas .I can take out two windows, the frames are re-inforced with mesh and bars+wire for light and ventilation. (There's a light inside for our benefit)
They have a rabbit hutch (on the floor with a door cut out) and a big plastic trunk (witth doors) as the sleeping quarters and floor space.
My piggies didn't like ramps (GP1/GP2) so we removed it (it went up to the top of the haybox)
The haybox is where they'll spend 99% of the time and the hutch has a fairly small haybox. You can maybe move the inner wall but you need to make sure they can use the ramp.
Are you planning putting it on grass? Or slabs? On grass you'll need to move it about. And it'll need to be secure so it doesn't get knocked over.
And secure the floor tray , there's a thread on here about a fox getting access.
You need to have access to the piggies regularly - inside they're accessible.
I think (personally) that my little ratbags like being outside , hearing everything going on. They are inside for winter nights though.
I've tried most beddings-mine like hay and lots of it 
Inside though I either give fleece on newspaper and haycookies or hay in a box. Or it will get everywhere. Tarpaulin on the carpet and a hoover round.
Boars or sows ? Or a neutered boar+sow/s?
Boar + sows is the most natural set up but it involves surgery for a little rodent. Lots of Rescues will do this, you pay a bit more (I paid IIRC £50 for GP6 - £10 for him and £40 for the op. Best £50 ever according to GP6 )
Boars are lovely and snuggly - just be aware of issues with space and their pecking order.
My sows are more independant ( in GP5 case that reads stroppy
) and pee loads.
And you'll get into The Neverending Spiral of when one dies, you get a new piggie... and so it goes on.
Read up on their food requirements.
Their potential illnesses.
Seek a Guinea-Savvy Vet . You might not need them , but it's good to know where they ate.
Three guinea-pigs would need at least 5'x2' in theory. In reality , it's not enough. They like lots of houses and space to get out of each others faces (especially boars)
Then they'll cram their massives rumps into a tiny box of hay and look gormless at ya.
Can you tell we love our piggies 