Scratch building is the process of building a scale model from raw materials or even materials found about the household, rather than building it from a commercial kit or buying it pre-assembled.
Scratch building is easy, if original plans of the subject exist. However because of the lack of plans, many models have to be built from photographs by measuring a known object in the photograph and extrapolating the rest of the dimensions. The necessary parts are then fashioned out of a suitable material, such as wood, plastic, plaster, clay, metal, polymer clay, cardboard or even paper and then assembled. Some purists consider a model not to be truly scratchbuilt unless all of the parts were made from raw materials. However some modellers consider a model including commercial detail parts as being scratch built.
Scratch built buildings by Duncan MacRae (EMRC)
Raw material including commercial detail parts shown before painting