We present a new and original approach for the fabrication of diamond MEMS using MPCVD. This process does not rely on diamond etching using conventional techniques such as e. g. RIE: here our MEMS structures are geometrically defined using silicon moulds in which diamond is grown selectively. The moulds can be prepared from silicon using DRIE and enabling a wide range of geometries. The critical point is the selectivity of diamond growth which dramatically depends on the nucleation process. Two nucleation methods for selective diamond growth inside silicon moulds were explored in parallel and compared, namely, the bias enhanced nucleation (BEN) and the nano-seeding technique. With both methods, MEMS structures were successfully fabricated and characterized, leading to values for the Young modulus above 830 GPa, thus comparing well with literature values. We believe our approach will ease the routine fabrication of large area diamond MEMS wafers for improved advanced device fabrication.