When looking for bearded dragon cages, it is best to find a cage that will best fit your dragon for its size at the time of purchase. Then as your dragon grows up scaling his new cage to fit his growing body will help keep stress levels low throughout your dragons life. This can be expensive and most people prefer to buy bearded dragon cages that will last the life time of the dragon.
A 55 gallon aquarium seems to be the aquarium of choice for most bearded dragon owners, however 55 gallon fish aquariums are narrow and dont allow much room to let your sprawl out in all directions. Most pet stores now carry reptile specific cages that are wider and not so tall allowing the owner to reach in easily to access the dragon, the waterdish and food bowl.
Custom built bearded dragon cages usually are the best choice as they can be made to specifically suit the needs of your dragon. They can also double over as a nice peice of furniture in your house. Custom built bearded dragon cages should be made so they can handle occasional misting and cleaning. Do not use treated lumber as it contains toxic chemicals that will kill your dragon.