Buying a cage is the largest expense in buying a rat but it is also possible to build a custom cage from relatively cheap items.
As a guide, the minimum floor space of any cage for 1-2 rats should be 2 foot x 1 foot, with at least an extra square foot of floor space for each additional rat. It is important to provide the best and largest cage for your rat(s) that you can as this is likely to be where they will spend much of their time.
There are a variety of rat, rodent cages or guinea pig and rat cages available from pet shops or Online Pet Stores which are suitable for rats. The most common type of rat cage has a plastic base and a rigid wire top. The wire top can be unclipped from the base making it easy to get the rat out of the cage or to clean the cage. Similar cages with two or more floor levels are also available with ladders which allow the rat to climb up and down between the different levels. These plastic base, rigid wire top cages are lightweight, durable and relatively cheap. However, you should check the secureness of any doors on such a cage as one that is opened too easily may be pushed open by the rat. A cage with a shallow base will allow woodshavings to be kicked out of the cage and so it is best to find a cage with a deep base. The disadvantage with these type of cages is that they are not draughtproof and so it is important that this is considered when deciding where to put the cage.
There are also various makes of cages which consist of solid compartments and tunnels. These cages are usually designed for smaller rodents and not suitable for rats as the tubes are too small for full grown rats to climb through and do not provide adequate space for the rat to move around.
Aquariums can also be used to house a rat. These are draughtproof and relatively cheap but glass aquariums can be awkward to clean because of their heavy weight. Plastic aquariums however are much easier to clean being lighter but the sides tend to become scratched after a time. Aquariums make ideal cages for pregnant rats, nursing mothers and baby rats. A water bottle can be fixed to the side of an aquarium by using adhesive Velcro pads or some water bottles are designed to be hung and these can be hung from the top of the aquarium. It is always best to ensure a lid is fixed to an aquarium - this will ensure nothing is accidentally dropped on the rat, and will also help in preventing the rat to escape - most full grown rats are able to escape from aquariums which do not have lids. A wire mesh top is preferable to a solid lid with airholes as this prevents the build up of condensation.
Cages made totally from metal are rarely seen these days and have a tendency to rust.
Home-made cages can be made from a combination of wood and wire mesh and a piece of perspex - the base, back and two sides made from wood, a front perspex window and a wire mesh top within a wooden frame hinged at the back and with a little securing hook at the front. The disadvantage with this type of home-made cage is that the wood soaks the urine and so frequent cleaning is needed to keep the cage free from smell and rats do tend to gnaw the wood and so these types of cages may need repairing from time to time.
Home-made cages can also be made from plastic storage boxes with wire mesh tops and these are cheap to make, easy to clean and draughtproof. The disadvantage is that they are usually solid coloured and so do not allow you to see the rat unless looking from above.