Permanent magnet direct drive (PMDD) electric machines are advantageous due to higher efficiencies and lower maintenance concerns. For wind turbine generators, especially offshore turbines, this is advantageous to geared machines and is currently implemented by manufacturers such as GE, Siemens and Enercon. By nature, a direct drive machine must be larger than its geared counterpart in order to output the same power. As a result, the structural mass is larger and makes the machine prohibitively large. However, the structural mass and electromagnetic design is coupled and the electromagnetic criteria are an important consideration in the structural design. In this analysis, the electromagnetic design of a 5 MW PMDD generator was coupled to a triply periodic minimal surface (TPMS) lattice generator through means of an evolutionary algorithm. Finite element analysis (FEA) was used to determine the radial, torsional, and axial deformations under simulated wind turbine generator loading conditions subject to critical deflection criteria. Lattice functional grading was completed with the FEA deflection data in order to further optimize the structural mass. For the 5 MW test case, functional graded TPMS support structures maintained stiffness for a generator with a 32% higher force density with inactive mass 4% lower than baseline. This study suggests functional grading of TPMS lattice structures for wind turbine generators has the potential at significant mass savings.