This paper presents lateral buckling failures of laterally unrestrained steel cantilever roof of a tribune with slender cross section under snow load. A structure located in eastern part of Turkey, and collapsed on October 25, 2015 is considered as a case study. This mild sloped roof structure was built from a variable I beam, and supported on steel columns of 5.5 m height covering totally 240 m(2) closed area in plan. The roof of the tribune collapsed completely during first snowfall after construction without any indication. The meteorological records and observations of local people are combined together to estimate the intensity of snow load in the region, and it is compared with the values specified by the code. Also, the wide/thickness and height/thickness ratios for flange and body are evaluated according to the design codes. Three dimensional finite element model of the existing steel tribune roof is generated by ANSYS commercially available software, considering the project drawings and site investigations to determine the buckling modes and related buckling loads. The analytical solutions of the cantilever beam are carried out and buckling load are obtained as q=22.236 kN/m(2). To validate the analytical solution using finite element analyses, one cantilever beam is modelled separately with roof slope. At the end of the analyses, the buckling loads are obtained as q=22.440 kN/m(2). It is seen that there is a good agreement between the results and maximum difference is attained as 0.91%. After the finite element analyses considering full system, the buckling load is obtained as q=31.00 kN/m(2). The failure mechanism using buckling mode shapes is very similar to site investigation. The obtained results are lower than the derived snow load considering field investigation. These results can be evaluated as the evidence to explain the reason of failures. The experimental, numerical and analytical works conducted in this study indicate that the snow could be trigger of the collapse, but not alone the main reason for this situation, with the combination of inadequate section properties, faulty design and workmanship errors during construction. (C) 2016 Elsevier Ltd. All rights reserved.