In most cities you buy a house from the count. in the castle. (Edit) In anvil it is different, you purchase the manor from Velwyn Benirus who is in the count’s arms inn in Anvil. Buying this house starts the Where Spirits Have Lease quest. In Skingrad you do not buy the house from the count, you buy it from his steward, an orc by the name of Shum gro-Yarug.