Body-in-White (BIW) is the Car Body without additional subsystems. Automakers are trying hard to reduce the mass of the vehicle body. The efficient option is to use multi materials and minimal number of parts in the BIW, in order to meet the stiffness requirements considering different load cases. Bending Analysis and Torsion Stiffness Analysis was performed to understand and assess the structural performance of the BIW. This paper presents the new BIW architecture with minimal number of parts, with an effective load path for the Structural and Crash load cases. Structural bending and torsion stiffness of the BIW were performed to evaluate the stiffness of the BIW to meet the passenger segment car. The methodology of using different materials for upper and under body has been investigated with the alternatives as Aluminium and Magnesium. BIW was analysed with Steel under body and Magnesium or Aluminium upper body. The Torsion stiffness of Steel/Magnesium BIW was found to be better than Steel/Aluminium BIW. The design concept with Steel underbody and Magnesium upper body was giving lighter weight design with better structural stiffness as compared to the Steel/Aluminium body. This approach of modifying the materials for the upper body of the BIW can be considered as lightweight solutions in other Conceptual BIW designs.