Now that you have provided an outdoor cat house, If you do not want to get annoyed at having to let your cat out when it wants to, then you should think about getting a cat door. The simplest cat doors, or cat flaps are just plastic flaps - easily blown open by the wind unless weighed down, or installed with a magnet. The flap could also be replaced with harder materials, but the principle is the same - when your cat gets used to the door, it uses it to go out and come back in as it pleases. Knocked over items, scratched furniture, potty accidents - these are some of the problems cat owners avoid when they have cat doors installed in their homes.
Unless you own many pets of varying size - big dogs and cats - you only need a cat door that's right for your cat's size. A flap is just a short passage way - both animals can use it. All they have to do is push on the flap to open it. Some flaps can be set to open only to one side, such as towards your house's interior, or exterior. You have to keep in mind, now, that because your cat can come and go as it wants, so can other animals (or small kids) of roughly the same size. You should get a different kind of cat door for that.
If you want to avoid having stray cats or dogs or other intruders - including small kids and thieves - you should look into automatic or electronic cat doors. The same principle is used in automatic dog doors, which makes use of a devices in the cat's collar and in the door, which "interact." The door opens upon sensing a device worn by your cat - a special collar; that way only your cat get in or out. Remember, you don't want uninvited animals pooping inside your home, stealing food, ruining furniture, or engaging your cat in territorial wars. What triggers the electronic door can be an infrared, radio, or magnetic device.
You may need to train your cat to use the cat door. Just show your cat how the flap works - push it open for the cat to see up close. If you installed a full-automatic cat door, you must make sure your cat wears the special collar that activates the doors. Your cat has to get used to the event - of the door's opening - as linked to his vicinity to it. You may have to use some enticement, like treats, to let your cat be comfortable seeing and using the cat door.
Installing any one of these cat doors is one way of taking advantage of the 'discount cat furniture' that is available today.