If the player lands on an unowned property, whether street, railroad, or utility, they can buy the property for its listed purchase price. If they decline this purchase, the property is auctioned off by the bank to the highest bidder, including the player who declined to buy. If the property landed on is already owned and unmortgaged, they must pay the owner a given rent; the amount depends on whether the property is part of a set or its level of development. When a player owns all the properties in a color group and none of them are mortgaged, they may develop them during their turn or in between other player's turns. Development involves buying miniature houses or hotels from the bank and placing them on the property spaces; this must be done uniformly across the group. Therefore, a second house cannot be built on any property within a group until "all" of them have one house. Once the player owns an "entire" group, they can collect "double" rent for any undeveloped properties within it. Although houses and hotels cannot be built on railroads or utilities, the given rent increases if a player owns more than one of either type. If there is a housing shortage (more demand for houses to be built than what remains in the bank), then a housing auction is conducted to determine who will get to purchase each house.