Structural Design for Walls & Floor of 2nd Story Addition to Garage

I have existing plans for a new home that is being built. I have decided to add a 2nd floor above the garage. Just need someone to do the structural support designs for the walls and 2nd floor system. Will need a steel beam in the middle I'm sure. The foundation is already complete with reinforced slab and can easily hold the additional weight. There will be stairs in the back of the garage going up to the 2nd level starting from right to left. I can provide all current files.