|This article is about an older version of DF.|
To build a smelter you need to use a fire-safe material, one stone or block. The construction is then a two-step process - first a dwarf with Building Designer skill enabled will bring the chosen material and design it via the Architecture labor, and then a dwarf with the relevant construction labor enabled (masonry for rock or rock blocks, any metalworking-type skill for metal) will perform the actual construction. These can be but need not be the same dwarf. Using dwarves with no skill training will get the job done, but will result in buildings of slightly less architectural value.
You place a smelter building using the keyboard commands --, after which your architect dwarf designs it and then your craftsdwarf builds it.
There is also a magma version of this building, which is built over magma and requires no fuel. Note that the process of making pig iron or steel will still need one unit of charcoal or coke per reaction as a reagent.