Well... If I was to run a game in a more core 4e game, but with my own twists.
Architecture:
Elves: In urban environments Elves tend to find areas isolated from major population amounts. It is common to see Elves living inside abandoned buildings, sewers, deep and dark alleyways, etc. These isolated areas are cultivated by the Elves both naturally and through supernatural means; vines, plants, ivy, fungus and the beginning of trees cover the area. Spores and fireflies light them up in a unearthly green glow.
Eladrin: Their structures are mysterious and hide in the corners of our eyes. Their towers grow out of the buildings of human cities, only visible as moon light streaks through it. Their doorways only visible through a blacked out mirror, etc. They exist everywhere but under the cover of illusions or in the shifting borders of the Feywild. Though the architecture is subtle and resembles the city they reside in, arcane markings and shifting and sentient thorny vines cover them.
Tieflings: Tieflings do not have an architecture of their own, however, they do choose certain areas. They prefer areas without many people and generally isolated. They tend to inhabit areas with other Tieflings. Their houses and businesses commonly have bars on the window and heavy metal doors for protection against the Churches.
Some I thought up right now.
