Cages
So, now you have your rats, where do you keep them?

There are two main options for the housing of rats: cages or tanks/aquariums.
In general, a cage is preferable over an aquarium for a number of reasons. The main reason is that tanks don't allow for good ventilation and rats can suffer from respiratory problems at the best of times. Because of this, you will need to clean a tank much more often than you would a cage. Also, tanks don't leave much space for adding toys, and even the biggest tank you can find will not be as big as the biggest cage!
I would only use a tank for nursing does or young babies. Very young rats should not be housed in cages as they can easily get their foot caught in the wire and cause injury and also, they'll try to climb which, if they fall, may prove hazardous for a baby. A tank will be good until the babies are weaned and ready to go.

Aside from any vet's bills, the cage will be the biggest expense in owning a rat and it's worth spending a bit of cash and getting something good than scrimping and having to upgrade the cage later anyway.
Some pet shops have been reported to be reccomending hamster cages as suitable for rats. Be very warey of this, and do not blindly trust the workers at the pet shop. A lot of them do not know anything about rats and assume they have the same requirements as a gerbil or hamster.
They do not. A rat's caging requirements are more akin to that of a ferret or chinchilla. They need a lot of room and the bigger the cage, the better.

It is truly heart-breaking when I get a rat come into my sanctuary that has spent it's whole life in a cage designed for hamsters where it has barely any room to move. Consider that your rats are as intelligent as a toddler, which will give you some idea of how much space and activity they need.

Steer clear of cages made from galvanised metal and these tend to smell bad after a time and are almost impossible to ever get smelling sweet again! Plastic or powder coated bars are the way to go!
I have gone through many cages over the years, some good, some not so good. Currently, my largest cage, where my boys live, is actually 6 cages all combined. I found I could pick up the large, ferplast or savic guinea pig cages for relatively cheap at car boot sales. I was also given a large cage that was two freddy cages wired together.
As my number of male rats increased, I gradually added more and more extensions to my original cages to the point where my boy's cage spans the entire back of the shed and reaches to the ceiling!

With a bit of DIY, you can customise pretty much any cage on the market to join it to another. I have found this to be the best option if you have a lot of rats, since there are not many cages on the market which are big enough for a large colony.
I simply cut away some bars with wire cutters, blocked the resulting hole with plastic tupperware lids so the sharp edges were not accessible to the rats, then used a stanley knife to cut circles in these lids.
I then simply pushed plastic tubes through them, and the rats now run back and forth between the 6 cages available to them.

Cages for small animals can be something of a rip-off when you consider the actual work that goes into them. Its not uncommon to pay over £100 for something that is literally just a plastic base with a wire frame on top! Therefore, I do always reccomend searching for second hand cages. You can find some good deals like this, and if you get something cheap, you can try customising it yourself and it wont matter too much if it all goes wrong!

Litter/bedding
For litter, most pet shops will still advise using woodshavings, but these are not suitable for rats.
Wood shavings contain oils called 'phenols' which damage your rat's respiratory system over time, so they should not be used in the long term. Unfortunately, most pet shops don't realise this so will still reccomend shavings as a suitable substrate.
There are far better options these days.
Paper based cat litters are safe for rats, providing they do not have any perfumes added to them. Steer clear of anything with added perfumes, chemicals or oils. Remember, rats have delicate respiratory systems.
One brand of paper based cat litter which I highly reccomend is 'Bio-catolet'. It is available from Tesco, and most pet shops. It comes in a green bag with a grey cartoon cat on it. The pellets are small, grey and look like compressed paper, which is what they are! Recycled paper is the one and only ingredient in Bio-Catolet, and it is very good at controlling smell.

There is also a litter called 'Carefresh' which comes in a pink bag. This, too, is a paper based product, but is lighter and fluffier than Bio-Catolet. Some people swear by Carefresh, but I've always found that it doesn't control odour as well as Bio-Catolet, and the light, fluffy nature of it means it is more easily strewn around and thrown out of the cage. It is also rather pricey, but if you only have a few rats, its a safe, easily available option.

Always make sure you only use PAPER based cat litters. Clay based litter could be dangerous if your rat ingests it.
Another very popular litter at the moment is a brand called EcoPetBed, which is corrugated strips of cardboard intended as horse bedding, and it comes highly recommended. Unfortunately, it isn't very easy to source in the UK at the moment.

For bedding, do not be sucked into buying over-priced, tiny packets of shredded paper or cotton wool. They are rip-offs. For a start, any fluffy, cotton-wool type bedding should be avoided anyway due to the risk of the tiny fibres becoming wrapped around the rat's limbs and injuring them. But as well as this, buying some rolls of cheap kitchen paper and shredding them up for your rats is just as good, and a lot cheaper!
You can also use pieces of fleece in their houses and beds. These are particularly good for elderly rats who move less and need a more comfortable bed. They will need to be washed or replaced regularly, though.
Hay is also a good bedding for rats. Its warm and is more natural for them as they can build proper nests with it, and even nibble on it.
Ensure it is good quality hay, and not dusty. It may also be beneficial to freeze the hay for a period before use, as hay can contain mites which will pass to your rat. Freezing it before use will kill them off.
If you have hairless rats, be extra careful with your hay. It can sometimes have sharp bits in it which, while they may not bother furred rats, can be uncomfortable for hairless ones.
Some people do not reccomend hay as a bedding because they fear it can cause eye injuries if the strands poke the rat's eyes, but I've never, ever had an issue with this and do not consider it a valid concern.

Toys
Rats love toys and are very intelligent animals, so you should provide them with things to keep them amused. Scientists estimate that rats have the intelligence of a 2-3 year old child, so its worth bearing this in mind when considering toys. A bored rat is an unhappy rat.
Rats love hammocks and no rat should be without one! Once they have it, you won't be able to get them out of it. I have several, so that when one is in the wash, they still have another to go in.
Hammocks can be purchased at acrorats.co.uk and Hammocky Hammocks, as well as lots of other places.
Im a big fan of HammockyHammocks, and get most of mine from them now.
If you have rats that like to destroy everything you put in their cage and don't want to spend money on something they will chew to bits a few days later, you can make your own hammocks out of towels/pieces of fleece and some clips. If you're a rat owner, it's a good idea to search charity shops for old fleeces and jumpers that you can cut up to make beds and hammocks!

The toy preferences of rats seem to differ depending on their gender, and age.
As females are more active then males, you tend to have a greater toy choice with them. Girls seem to like toys that allow them to climb, so shelves, ladders with dangly things attached, tubes, jingly balls, rope bridges and such are all favourites with girls.
Boys, however, can be downright lazy. They prefer toys they can sleep on, or in! My boys like shelves and tubes, like the girls do, but they seem to get little excitement from ladders, branches and rope bridges. They prefer houses they can hide in, log bridges they can sleep under, and fluffy, fleecey round beds.

Of course all rats are different, so try everything and see what your rats happen to like using most. Young rats are more likely to get the most out of toys, some old males will completely ignore them!

Rats can be given wheels to run in, but there are a few things to bear in mind before you run out and buy one.
Firstly, a lot of rats will completely ignore a wheel and never use it. You'll probably find that females, and very young males, are the only rats who will run in them. Occasionally there are exceptions to this, but for the most part, adult males will only use them to sleep in, if that.
Secondly, there are only two makes of wheel that I would ever use for my rats. They are the 'Wodent Wheel' and the 'Silent Spinner'These wheels are designed specifically with rats in mind and are 100% rat safe.
Most other wheels are either far too small, or have wire rungs on them which rats can trap their tails in. Remember, an animal running in a wheel should have its back pretty much straight as it runs. If it's back is curved into a 'U' shape as it is running, the wheel is too small.
The largest size 'Silent Spinner' is a good wheel for girls. My girl's have one, but only 2 of them use it. The largest size 'Wodent Wheel' is a good wheel for bucks. But again, be aware that an adult buck who loves to run in a wheel is a rarity. You may have better luck if you introduce them to it as babies, however.