scratch-built
Adjective
Meaning
Of a building: built ad hoc, with whatever materials are to hand, and often just from ground level.
Of a structure, e.g. a car, model or toy: built with minimal cost and at short notice, with rudimentary materials.
Source: en.wiktionary.orgExamples
Most Jeepneys today are scratch-built by local manufacturers, using different powertrains.
Z scale (1:220) scene of a 2-6-0 steam locomotive being turned with a scratch-built Russell snow plow parked on a stub (Val Ease Central Railroad).