The recent advances in nanofabrication techniques have given a boost to the study of artificially patterned magnetic films for future applications in high density magnetic storage, sensor technology and magneto-logic devices. Attention has been focused on the dynamic properties of magnetic antidot arrays (magnetic films with embedded holes), which can be exploited for the design of magnonic-crystal waveguides, spin wave emitters and nanoscale microwave filters [1-3]. Their ferromagnetic resonance (FMR) behavior is strongly influenced by the lattice geometrical properties, which can be artificially tuned by modifying the shape and size of the non-magnetic inclusions, as well as their arrangement and packing fraction [4]. In such scenario, the accurate control of geometrical properties at the microscopic level is of fundamental importance to avoid alterations of the expected magnetization dynamics and resonance modes.