CoD style weapon selection

Hello, I was wondering how you would script a CoD style weapon selection system where you could either pick up weapons along a level, or have a GUI in the start menu where oyu could select a primary, secondary, and grenade. Any sample scripts or links tutorials would be really helpful. I have looked all over the place for sthuff like this and I can't find it anywhere so I think this would be a great help to the unity community.