Here are some architectural ideas I used in my old 3rd Edition Campaign
Dwarven Architecture:
Dwarves dwell principally underground, although every Dwarven city will have a few aboveground towers that serve as the headquarters of the various Companies that control Dwarven life. These towers are often up to 100 feet high, square or octagonal, and taper slightly from bottom to top. Below ground, Dwarven settlements always feature a massive central hall. Above or below ground, all Dwarven structures feature extremely high ceilings, at least 15 feet or more.
Dwarven architecture is notable for its sharp clean lines, stark lack of ornamentation, and avoidance of round shapes and surfaces. Pillars, for example, are always polygonal in cross section, rather than round. Dwarven structures always look imposed on their environment, and Dwarves believe this is proper. Organic forms and shapes are considered degenerate. The Dwarven ability to work stone into a continuous, smooth and unblemished surface is unmatched by any other race.
Gnomish Architecture:
Gnomes prefer to live as close to the Earth as possibly. Their ancient ancestors lived in burrows, and the typical Gnomish home is inside of an artificially created mound of compacted earth. A door and windows will be cut into the sides of the mound, which is almost always covered with grass or other plants. Inside, the mound will be richly and beautifully finished, usually in wood stained to bring out the natural grain. Atop the mound will be a garden, often accented with sculptures, or oddly shaped rocks. Monumental buildings are simply larger versions of the ordinary Gnomish burrow, housed in correspondingly larger mounds.
When dwelling in human cities, Gnomes will always seek to inhabit either the basement or ground floor of a building.
Orcish Architecture:
The basic Orcish structure above ground is the hovel, crudely made of rough-hewn logs caulked with mud, moss and blood. A hovel that has no blood in its caulking is considered extremely unlucky. A village will consist of a ring of hovels, enclosed within a log palisade. Many Orcs choose to live below ground instead, in caves or excavated strongholds. Common Orcs have no monumental buildings, since religious worship centers on the communal campfires, and chiefs simply have larger versions of the same hovels that all other Orcs live in.
Orcs love swirling designs, and swirls of some form are often carved or painted on the walls of Orcish dwellings.
