Step 1 - Measure. Determine how wide the headboard should be. Since I am building this one for a queen mattress, and am going to have the outer posts go all the way to the floor for extra support, my inside (between the posts) measurement is 65". The height measurement is personal preference - how high do you want the headboard to be?
Step 2 - Frame. This frame is the base for the headboard. I built the frame according to the measurements taken in step 1. Lay the frame out square on the ground and screw together. (If you have a nail gun, use it.)
Step 4 - Doors. My cabinet doors had to be cut down to the same length since they were not all the same. Pre-drill holes into the doors so the screws will be counter-sunk. Secure these doors to the frame with screws.