The next step in creating this bar is to add stabilizers to the top plate to ensure stability in the bar. By adding several 2X4s to the top of the bar you will create a spot to fasten the MDF board to. Cut enough pieces that you can have one stabilizer (one board) over each stud on the main framework. You will want to cut this piece as long as you want the bar top to be. For me we cut ten inches for the portion of the bartop hanging over the front and 8 inches for the bartop hanging over the back.
Doing some basic math. 10" hanging over the front + 3-1/2" (for the top plate) + 8" hanging over the back = 21-1/2" <---- Cut enough of these to sit on top of each stud on the main framework.
Use four (4) screws to attach these stabilizers directly into the top plate. They will create a spot to put the bartop.
NOTE: The picture below has the MDF board attached!