There really is no limit to the styles and designs you can achieve when using metal curtain rods. You usually think of modern window treatments when it comes to meal, but you can create very traditional looks using classic brass and bronze with ball finials or end caps too. While metal rod diameters are usually smaller than their wood counterparts, as long as you install brackets every three or four feet, metal rods will do a great job supporting the weight of your fabric.
Metal curtain rods are typically round and smooth poles. You won't find fluted, twisted or grooved options like you may see with wood or wrought iron style. There are some unique square drapery rods with coordinating geometric rings if you're interested in something a little different. Metal rods are sometimes manufactured as adjustable poles. Adjustable rods are handy because you can resize them at home to get a perfect fit for your window. Just keep in mind that adjustable rods are usually not as strong and durable as solid poles. So if your curtains are heavy, you may want to get a rod whose smallest width more closely matches your window size so you'll have double strength across your span.
You might notice some wood style components or poles mixed in with metal drapery hardware collections. That's because it's popular to mingle metal components like finials or brackets with wood style poles. For example, you might want to use a shiny chrome end cap on a dark stained wood pole for a stunning design.