Keep your outdoor fireplace clean and safe
The level of maintenance that will be required of you for your chiminea outdoor fireplace will vary hugely depending on the material type that you choose to purchase. Many of the fireplaces that you buy at large department stores are of either the plate steel or sheet metal types. Plate steel is a reasonable material, but sheet metal generally isn't. Although plate steel fireplaces are bulky enough to be fairly resistant to moisture and elemental exposure, they are still prone to rust (although less so than cast-iron) and they are generally less aesthetically appealing than one-piece cast-iron or cast aluminum models.
The single most maintenance-free chiminea material is cast aluminum. Because aluminum does not rush, your maintenance requirements for this type of chiminea will be reduced to clearing away branches and leaves and ensuring that the lid is placed over the chimney opening to keep dirt and grime from pouring into the firebox from the top. With clay or terra cotta chimineas, there is maintenance involved in every use – you must gradually warm the chiminea, keeping the fire low and incrementally increasing it so as not to crack or damage your outdoor fireplace. Copper chimineas require frequent scrubbing and polishing to minimize the formation of green oxidization (rust). If you like the look of tarnished green copper, as some people do, then you won't have to worry about this.
Cast-iron chimineas are the heaviest and most rust-prone, but they are also the most heat-resistant and generally have the longest life expectation. These chimineas can even be used in the winter without damage. However, they are also more expensive than their cast aluminum counterparts, which are made with the same molds.
Realistically the best bang for your buck in terms of minimal maintenance and long life is a cast aluminum chiminea. If you plan to keep your chiminea at a camp site or other area with minimal supervision, the additional maintenance requirements of a 200-300-lb. cast-iron chiminea may be outweighed (no pun intended) by the difficulty in moving or stealing it. Otherwise, stick with the lighter and easier to care for aluminum version. Of course, if your main goal for an outdoor fireplace is heat, you may be better served by a patio heater.