A nacelle for a wind turbine and a method for erecting a wind turbine are disclosed. The nacelle comprises a main unit arranged to be connected to a wind turbine tower, via a yawing arrangement, and at least one side unit mounted along a side of the main unit in such a manner that direct access is allowed between the main unit and the side unit(s), each side unit accommodating at least one wind turbine component, and at least one side unit being capable of carrying the wind turbine component(s) accommodated therein. The main unit and at least one of the side unit(s) are distributed side by side along a substantially horizontal direction which is substantially transverse to a rotational axis of a rotor of the wind turbine. A sufficient interior space of the nacelle is obtained while allowing the nacelle to be transported due to the modular construction. The weight of the wind turbine components is arranged close to the tower due to the transversal arrangement of the side unit(s) relative to the main unit.