Aesthetics of a structure are given primary importance in the present days and this demands new and challenging designs with large spans and complicated designs. The role of a structural engineer becomes more significant because of these structural irregularities. This makes it necessary to have advanced technologies like post-tensioning if we are not ready to compromise in the aesthetics. Generation of such irregular structures will form varying mass and stiffness distribution which imparts to the effect of torsion. This paper deals with the various structural behaviour of a multi-storied RC Convention Centre building having large spans of around 32 m. The effect on the structure due to these large spans is compared with both RC and prestressed concrete. The roof slab of the auditorium portion of the structure is designed with normal RCC and compared with Slabs resting on Prestressed Post-tensioned Girders using the software Adapt Builder 2016. A comparative study between RCC and prestressed concrete is also done. Diaphragm action of the structure is considered for seismic design in order to provide a monolithic action and hence to counteract the effect of torsion. A comparative study is done with and without considering the effect of torsion into account and the results shows that in higher seismic zones the effect of torsion is predominant and proper care should be given to extreme columns and corner columns which are more vulnerable to failure. Response spectrum analysis of the structure is done in STAAD.Pro and storey response plots are obtained. © Springer Nature Singapore Pte Ltd. 2019.