The idea that rats are dirty and mean is a common misconception. This may be true about sewer rats or swamp rats who live in filthy places but it is false when referring to pet rats. Domesticated rats are intelligent, curious, friendly and entertaining. Rats found in pet shops are descended from the Norwegian or brown rat. They are small and have been bred over the years to be suitable pets. Their color ranges from white to black with many shades in between. Pet rats are actually one of the cleanest rodents you will find in a pet shop.
When planning to have a rat as a pet it is important to be careful to pick one that is healthy. Signs of a healthy rat include bright and clear eyes, curiosity when held, and quiet breathing that can only be heard if the rat is sniffing your ear. Rats are most likely unhealthy and should not be purchased if it has red mucous around the eyes, it is sniffing, wheezing or coughing very apparently, it has bare patches where there should be fur, or if it is lethargic when held and seems to have muscle weakness. Don’t purchase a sick or unhealthy rat thinking that you can nurse it back to health. In most cases the rat will end up dying and you will have wasted your money or it could have some illness that will cost lots of money in veterinarian visits to treat.
Rat cages should be at least a square foot on the base. The larger the cage the happier the rat will be in most cases. For each additionally rat there should be at least an additional one square foot of floor space in the cage. Cages with wire walls are best as they allow the rats to climb which they love to do. The gap between the wires of the cage should be smaller then the rats head so that the rat can not escape as rats are prone to do if the gap is any larger. Rats need a lot of toys to keep them occupied and entertained. They are not fond of rodent wheels. Their favorite toys seem to be puzzle toys where they have to figure out how to get the treat inside the toy. Rats also do not like hamster wheels.
Rats are not hard to feed. They are omnivorous and will eat nearly anything. That doesn’t mean you should feed them whatever is lying around the house. A rat pellet really will provide them with the best nutrition. You can give them a supplement of mealworms or fatless grilled chicken if desired but no red meat. Rat treats can be given but not too many or the rat will become overweight. Rodent bottle for water is important. A water bowl can be used if desired instead but it is not recommended as it is likely to get knocked over and used as a toilet.
Reference:
http://www.pet-care-portal.com/pet-rat-care.html