Hi Waqar,
I hope you have got your answer from sir Umer and others I will just add something as per my experience with the steel structures. In most cases cold form steel or light gauge structural members are designed on the basis of local failure in stead of global. These buildings are single storey most commonly and double to triple storey in very special cases. So the loadings are worked out manually and each member either column or beam/truss is checked for the local buckling and bending, axial and shear stresses. These members can be modelled individually in SAP 2000. The members are closely spaced to each other like wall panels may have studs at every 400mm c/c and then for door jambs and window head your section are doubled etc. So the steel in a wall section or roof members is quiet high.
For the modelling of these structures you must do these manual checks before and calculate the required capacities of each members and your required bracings etc. then you model the structure you will get the results. But still having said that the wall studs have many jointing elements like horizontal support members for the installation which are normally difficult to model and these restraining elements also help in reducing the KL/r for the elements. which is not considered in most cases during modelling. So the best is to do these structures manually and verify them by any software with logical assumptions. software like framecad are designed for these structures so they take into effect all the restraints as you build your 3d they add all the required horizontal supports due to which the analysis results are different to as modelled in SAP 2000.
Cheers,