Most hobbyists who build models of buildings do so as part of a diorama to enhance their other models, such as a model railroad or model war machines. As a stand-alone hobby, building models are probably most popular among enthusiasts of construction toys such as Erector, Lego and K'Nex. Famous landmarks such as the Empire State Building, Big Ben and the White House are common subjects. Standard scales have not emerged in this hobby. Model railroaders use railroad scales for their buildings: HO scale (1:87), OO scale (1:76), N scale (1:160), and O scale (1:43). Lego builders use miniland scale (1:20), minifig scale (1:48), and micro scale (1:192) Generally, the larger the building, the smaller the scale. Model buildings are commonly made from plastic, foam, balsa wood or paper. Card models are published in the form of a book, and some models are manufactured like 3-D puzzles. Professionally, building models are used by architects and salesmen.