Results of large-eddy simulations of stably stratified atmospheric flow around an isolated, complex-shaped tall building are presented. The study focuses on the identification of flow structures in the building wake in high and low Froude number regimes. A qualitative comparison of results with available literature data and existing theories is presented. In addition to flow structures identified in earlier studies such as the horseshoe and recirculation eddy vortices, we analyze a stationary disturbance akin to mountain gravity wave, and a complex vortex structure associated with this wave, consisting of multiple symmetric pairs of vortices. The Froude number appears to be the principal parameter controlling the structure of the wake, waves and vortex pattern.