I already have 3 guinea pigs and they go out in their run in the garden, would i be able to put the rats with them for half an hour or so. or is this a definite no no

thankyoo, keira x

No. Different species should not be allowed 'play time' together. Neither group will benefit, and you run the risk of injury to your pets. I've seen a rat chase an adult rabbit, and my older (neutered) male Tsume would actively chase/bite by dogs if they happened to be near him while he was freeranging. Rats can be territorial little buggers ;).

yeah, guinea pigs are so docile (they kind of remind me of tiny cows) i'd be worried about them with such a crafty, clever little rat in the room.

Nooooo! Rats would attack, or at least chase guinea pigs. Your guinea pigs would be terrified of the smell - rats are predators to guinea pigs so they're instictively afraid of them.

Just as a side-note, rats are pretty susceptible to diseases and illness, and letting them roam free-range outside is asking for ticks, fleas, and the infections and disease that come with those creatures.

I would also like to see the fence capable of holding a rat.

Just be careful I guess, and don't be surprised if you get itchy rats in the near future.