you can buy three plots of land:
Lakeview Manor (Falkreath),
Windstad Manor (Morthal) and
Heljarchen Hall (Dawnstar) To buy the plots of land you need 5000€ each and have the
Thane Status in all three cities, then ask the Servant of the Jarl (in Dawnstar the Jarl himself) about a house. After you paid 5000 € (each) you get a Misc Quest and a Map Marker.
You dont need to build the Houses, just buy the land. After you bought the 3nd one, you get the Achievement. If you need help with the Thane Status, check this Link:
http://bit.ly/Uq9mkP------------------------------------------------------------
usefull comments: --------------------------------------------------------------------
FreakOfTheAbyss: You CANNOT get the land in Falkreath if you have completed the Dark Brotherhood quests, as you have to kill a certain person that makes the Jarl always dislike you and therefore refuses to sell you land. Just a heads up for anyone else who got screwed like I did.
FreakOfTheAbyss: Did you kill the steward as part of the quest you did? I think you may be able to choose not to kill him, but if you killed him there is no way to get the land.