3D modelling in the inception phase of architectural design is typically not supported in CAD. Moreover 3D modelling is still far from intuitive with the common interface techniques. This paper introduces a 3D modelling tool for architects, named DDDoolz, which is limited in its purposes but yet very powerful in its use. A cube is the basic drawing element to construct arrays representing building masses. Modification of the design is achieved by dragging sets of cubes, resulting in the creation or deletion of new cubes. Building upon the grid structure of DDDoolz, a design methodology has been developed. To analyse its strengths and weaknesses, DDDoolz is compared with traditional scale modelling.