Houses are placed in the open world as opposed to the instances found in many MMOs, and XLGAMES has designated certain build areas on AA's northern and southern continents as well as several islands. Depending on placement, houses may be taxed or even destroyed. ArcheAge features several architectural styles including various Asian and Western influences along with the ability to build stilt homes on the water.
The guide touches on the game's castle system too, and apparently players will need to plan the entire layout since the location of walls, towers, and farms are not predetermined. Have a look at a 10-minute CBT4 housing construction video after the break, then head to ArcheAge Source for dozens of housing-related screenshots.
[Thanks to Dengar for the tip!]