A customizable portable generator system and methods for assembling the same. In one example, the generator system generally includes a universal frame including a plurality of mounting interfaces configured for detachably attaching one of a plurality of different engines and a plurality of wheel assemblies and/or support legs. Optionally, at least one handlebar assembly may be detachably mounted on the frame in at least one of two possible positions. In one example, the handlebar may be pivotably mounted to the frame. The frame components may be assembled into a kit from which a user may select various options to custom configure the generator unit. Other appurtenances and accessories may be provided which interface with the generator unit and frame. A modular generator frame and compressed gas-fueled generators are also disclosed.