Scratch building is easiest if original plans of the subject exist; however, many models have been 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, 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 most modellers would consider a model including commercial detail parts as scratchbuilt. Scratchbuilding a new body onto an altered ready-to-run chassis is also acceptable.