In order to add some support, as well as a spot for a shelf behind the bar we will create two or three block structures. See the picture below for extra help. Determine at what height you will want your self to be. For my bar I chose 26". Not unlike the first step in this design make three (3) pairs of 10'' 2X4s (these will act as top and bottom plates for the structure.
Doing some basic math for the "studs". I want the shelf to be at 26'' therefore, 26" - 3" (top and bottom plates) = 23" <--- this will be the cut for the studs. Cut two per structure (I would cut 6 because I am adding three structures).
You will assemble rectangle like structures out of the four 2X4s (two ten inch pieces and two 23" studs). Once you have these screwed together you will screw them to studs from are previous frame. (SEE PICTURE BELOW)