As wind turbines increase in power output, their size and mass grows as well. The development of offshore wind farms demands higher reliability to minimise the maintenance cost. Direct drive electrical generators offer a reliable alternative to conventional doubly fed induction generator machines since they omit the gearbox from the drive train. A fundamental issue for these generators is their large size which makes them difficult to manufacture, transfer and assemble. This study will investigate an analytical and a finite element analysis optimisation technique developed for minimising the structural mass of a direct drive generator. Both tools seek to minimise the mass of three different permanent magnet direct drive (PMDD) generators with 5 MW nominal power output while keeping a set of deflection criteria under limitations. The results indicate that the structural mass of a 5 MW PMDD generator can be effectively reduced with the help of these design tools. The research concludes in favour of a specific transversal flux PMDD topology, of which the electromagnetic topology benefits the structural design