The solution engine of MultiCAD-GA, presented in this work, is a part of a new software environment for efficient search for solutions in heavily demanding applications involving the design of three-dimensional forms, such as those of architectural and interior decoration design. MultiCAD-GA starts by using constraint programming techniques in order to find a set (population) of solutions (forms) that satisfy the spatial constraints imposed by the user and create an initial generation. In the sequel, it applies genetic operators to generate new solutions and interacts with the user in order to evaluate the solutions and increase the speed of convergence to those forms that satisfy his/her aesthetics. The forms are coded into chromosomes using the usual binary strings. Visualization of the results is performed through the VRML graphics language.