Here a method of multi-parameter optimization is used to create shell structures of constant thickness from linearly elastic homogeneous material. Our goal is to optimize a relatively complex shape of shell only by changing its geometry in a way to get better stiffness. We propose that a loading cases are not known exactly and so we use the criterion which on the basis of an arbitrary chosen eigenvalue frequencies, gives a stiffness of shell structure. The optimization algorithm is based on stigmergy, which is becoming increasingly popular in combinatorial optimization and lately also in multi-parameter optimization. The method was verified on a real industrial problem on an electric motor casing.