Buildings or Structures are generally fixed, functional, player-controlled constructs. The role of buildings is generally to enable the production of units and/or unlock higher tech and function, although a few specialised racial structures are meant to contribute to static defense. Certain buildings can potentially be moved in StarCraft, but lose their functionality while mobile (these include Spine Crawlers, Spore Crawlers, and Terran buildings with the Lift off ability).
They are generally created by Workers (viz. SCVs, Drones, and Probes) using different race-specific processes, but in some cases are created with other means: they include Creep Tumors and Add-ons, which are created by a non-worker unit's spell or another building.
All buildings must be constructed on "buildable terrain", which excludes all "off-map" terrain, other buildings and units, and certain map features, and includes Vespene Geysers in the case of gas buildings. Additionally, Protoss and Terran buildings may not be constructed on Zerg creep. Protoss and Zerg have other special requirements for building placement which are explained further below, with the exception of their townhalls, supply, and gas buildings. Upon the destruction of all of a player's buildings, a player may lose the game (see Stalemate Detection).
The Townhall is the most important building. It is where workers bring the resources they gather, and it is where workers are produced. It is also required to build the first production facility.
In each game, a player begins with a single townhall and six workers. These are the basic foundation blocks from which to build a base. For the different races, townhalls manifest as a Command Center (later upgraded into a Orbital Command or a Planetary Fortress), a Nexus and a Hatchery (later evolved into a Lair and then further evolved into a Hive).
These buildings serve to increase the total number of units a player can field at one time (until the maximum of 200 supply is reached). These buildings are the Pylon and the Supply Depot. Zerg does not use a building for supply, but instead uses Overlords, a flying unit that costs no supply to produce or maintain itself which serves the same function.
Supply is so named after the original name for Terran supply. Alternate names for these buildings are pop (population), upkeep, or food buildings, or the original names for Protoss and Zerg supply, psi and control.
Static defense buildings
See also: Static Defense.
These buildings are constructed to provide protection in a certain area. Their general purpose is to stop or at least to discourage an opponent from attacking that area, but they can often be used in tandem with an army. Some, such as Missile Turrets, or Spore Crawlers, may be placed around the base and especially around resource nodes specifically to provide detection.
These buildings are where the bulk of offensive units are produced. Terran and Protoss have dedicated unit-producing structures, whilst Zerg have their Townhall Building and Production Building in one, as all units are produced from the Hatchery (or its later evolutions the Lair and Hive).
These buildings open up new technology for a player, whether that be new units, buildings, and/or upgrades for units/buildings. Most buildings—even Production and Townhall buildings—fall under this classification.
Technology only buildings
Buildings that solely open up new tech paths, without offering any production.
Nearly all of Zerg's buildings are classed as technology buildings, due to the mechanics of the race.
These are buildings placed by the mapmaker. They are sometimes placed for decorative purposes, or a purpose within a Use Map Settings match. On competitive maps, most neutral buildings are Destructible Rocks, providing a new path for units to travel, to block High Yield minerals, et al. Some maps feature neutral Supply Depots, often to prevent walling off an opponent's ramp.
Racial buildings specifics
Each race has their own particular quirks when it comes to buildings. They are discussed below.
Terrans use their SCVs to build structures. During this process the SCV is occupied actively building the structure. A building can be built anywhere, provided the SCV can reach the location—other than the aforementioned terrain types (space, water, etc.).
Some Terran buildings have the ability to Lift Off, which lifts them into the air where they become mobile "air units". They move very slowly and are unable to produce units or use spells in this state. This ability is exclusive to the Terran race.
If a Terran building is damaged to below 1/3 of its maximum HP, it will catch fire and begin taking 3 damage per in-game second until it is destroyed or is repaired to above 1/3 of its maximum HP. This does not apply to buildings which are "under construction", that is, any building which has not been fully built, regardless of whether an SCV is actively working on it.
Protoss buildings are "warped in". A Probe is required only to place a building, at which point it warps in on its own and the Probe can move on. The key Protoss building is the Pylon. It provides a circular area of "power" in which other (non-Pylon) buildings may be built (only the Nexus, Assimilator, and Pylon are immune to this requirement.) If a Pylon is destroyed, all the buildings depending on it become "unpowered". Unpowered buildings lose their functionality until their power is restored by a new Pylon, though even unpowered buildings count towards technology requirements.
Zerg buildings are dependent on Creep. Creep is a substance that is spread on the terrain by the Zerg townhall (and other means). Zerg buildings must be built on creep and, if the creep is removed, buildings will slowly die, unless the creep is restored. On creep however, they benefit from regeneration. When a Drone is ordered to construct a building, it morphs itself into the building, and is lost. The Drone can be recovered by cancelling the building before it is completed. Upon death, Zerg buildings other than Extractors, Spine Crawlers, Spore Crawlers, and Creep Tumors will spawn several Broodlings.
All buildings come with the Structure, Armored and Ground attributes. All Terran buildings are also Mechanical, while all Zerg buildings are Biological. Some buildings also have the Ranged attribute; they are listed in the static defense section above.