we are suppose to define all the GUI requirement

In software Requirement Specification SRS document, if we have decided to include the GUI; then how we are suppose to define all the GUI requirement; developing a GUI in VC++ or even Visual Basic requires a lot of intensive programming and it is infact a design level stuff...In fact we are doing the job of the developer...then for what we are paying the developer for?

As you always read and listen that developing a software is a team work. If we need to include GUI in SRS,then it  is not done by requirement analyst/requirement engineer. This is job of designing team/designers. In this case, designers and requirement analysts work together to define and develop GUI according to requirements.