Housing & Cage size

One of the most important initial things to consider for your cockatiel is his cage. Regardless of how much time your bird will spend confined to the cage certain factors should be taken into account. It is paramount that your bird is safe, happy and comfortable.
The cage should be as large as possible. The height of the cage is less important than the width and length. Your bird needs to be able to flap its wings without risking injury. Ideally the minimum length and width should be 50cm. This size will give more room for your bird to fly from one side to the other. A taller narrow cage is not suitable.
The spacing of the bars is also very important. If the bars are too far apart then your bird may quite easily get its head between them and risk getting stuck. Or even worse your bird may escape. Horizontal cage bars also make it easier for your cockatiel to maneuver around the cage sides. Vertical bars are slippery and make it difficult for it to climb on.
Inspect your cage thoroughly before introducing your new bird to it. Look for sharp areas that may cut your bird and any loose wires or flakes of paint. It is a good idea to scrub the cage and all toys and feeding containers with detergent or vinegar first then it should be thoroughly rinsed and allowed to dry. This will ensure no harmful substances are present that can harm your bird.
A cage with a slide out tray and wire grate in the bottom is the best option. If a wire grate is between the bird and the floor of the cage then feedstuffs have a lesser chance of being contaminated by droppings. It also prevents your bird being able to access his own waste. The slide out tray can be covered in paper and slid out and the paper changed to make cleaning simpler and easier. Using something like paper towel in the tray also makes it easier for you to inspect your cockatiels droppings to make sure everything is normal.
Perches need to be firmly fixed and of varying diameters to give your birds feet exercise. The use of natural branches is a good idea, as it will also give the bird bark to chew off and tear apart. These can be easily replaced.
Position the cage away from draughts and direct sunlight. It is fine to move it to get the warm sun in winter but the hot summer sun even through an open window can cause stress on your bird. Draughts are more detrimental to your bird than cold weather. A place away from open doors and windows in winter and a cover at night will help keep your bird safe and warm.
Seeing your bird is a member of your family he/she needs to be near you. Don't put the cage in a remote lonely corner where it is away from everyone. A comfortable area in your living room where it can be a part of the daily activity is much more suitable. On the same note though don't have the cage in a busy thoroughfare where it will continually have children running past or be bumped.
If the cage is to be outdoors at any stage then care should be taken that all the doors and latches on it are working properly and the bird cannot open them. It needs to be placed in a position outside that is protected from the weather and not easily accessible to other birds and pets. Butcherbirds and crows are a very real threat to your pet as well as dogs and cats that may even be capable of knocking the cage over and freeing your bird.
Your bird will be happier if its cage is not sitting on the floor. Be it inside or outside a bird always feels safest when it is off the ground. It can see better what is going on and is less likely to be stressed by other pets or small children.
Last but not least please keep your birds cage clean. The build-up of droppings and old foodstuffs will only lead to attracting rodents or even bacteria and harmful parasites. If the tray is emptied daily and fresh food and water is given each morning then it saves a huge effort of having to clean a very big mess. The addition of a seed skirt around the base of the cage may assist in preventing your bird's mess from spreading too far a-field.

Credit:
http://www.members.optusnet.com.au/~geoffwatts1/index.html

Good job on finding this! Helped me too. For when I move I mean...