Breeding blankets are designed to ensure tritium self-sufficiency in deuterium- tritium fusion power plants. In addition to this, breeder blankets play a vital role in shielding key components of the reactor, and provide the main source of heat which will ultimately be used to generate electricity. The design of blankets is critical to the success of fusion reactors and integral to the design process. Neutronic simulations of breeder blankets are regularly performed to ascertain the performance of a particular design. An iterative process of design improvements and parametric studies are required to optimise the design and meet performance targets. Within the EU DEMO program the breeding blanket design cycle is repeated for each new baseline design. One of the key steps is to create 3D models suitable primarily for use in neutronics, but could be used in other CAD based physics and engineering analysis. This article presents a novel blanket design tool which automates the process of producing heterogeneous 3D CAD based geometries of the Helium Cooled Pebble Bed, Water Cooled Lithium Lead, Helium Cooled Lithium Lead, and the Dual Cooled Lithium Lead. The paper shows a method of integrating neutronics, thermal analysis and mechanical analysis with parametric CAD to facilitate the design process. The blanket design tool described in this paper provides parametric geometry for use in neutronics and engineering simulations. This paper explains the methodology of the design tool and demonstrates use of the design tool by generating all four EU blanket designs using the EU DEMO baseline. Neutronics and heat transfer simulations using the models have been carried out. The approach described has the potential to considerably speed up the design cycle and greatly facilitate the integration of multiphysics studies.