Note: Many owners consider it very dangerous to house guinea pigs on wire and it is really is much SAFER to house them on solid floor cages so these are the only choices many owners will consider. I.E. you take a risk if you chose to house them on wire flooring.
 

These two guinea pigs are kept on wire with  a second story resting place on top and one on the bottom filled with wood shavings.

This is an ideal way to provide water for guinea pigs, especially if they stay in wood shavings which can be kicked into a water bowl/dish.

This bowl is a bit too big for this guinea pig but he's still enjoying his meal! Guinea pigs will clinb into and may end up sleeping in their food bowls if they are too big.

Just like rabbits, some (but not all) guinea pigs can get used to using a litter box when they are away from the cage. You can buy one made for cats or you may be able to find a similiar item in the household departments of some stores. 

Pine and cedar have been said to cause liver and respiratory problems in guinea pigs and other animals. You might want to try a substitute. Presently, the only one that is readily available in Singapore pet stores is corn-cob . However, make sure that your pet doesn't take to eating it.

You can fill the litter box with cat litter (make sure it isn't too dusty) or those made for small mammals. Wood shavings tend to fly and stick on the guinea pig every time it comes leaves the litterbox.

Guinea pigs also have ever-growing teeth and require teeth trimming opportunities. If all they have to eat are pellets, they may not be using their teeth enough and they may overgrow. To prevent this and the sometimes destructive behaviour that follows their urge to trim their teeth, you can provide wooden or mineral blocks.