We went with the mission style headboard and used 1x2 posts instead of a solid or upholstered backboard. We also converted the designs to accomodate our California king mattress.
The designs on the site are for a queen sized bed, which is 60"X80". The "H" frame of the headboard is 66" wide (two vertical 2x6's and a 54" horizontal piece). Our California king mattress is 72"x84". So that's 12 inches wider than a queen. As such, we simply adjusted everything up by 12". So, insead of a 66" wide H frame, we made it a 78" H frame and so on.
It took just one day to build. But we used an entire container of woodfiller to conceal the joins, nail/screw holes and knots, lol. Then we used 2 coats of primer and sanded between coats. Then used 3 coats of latex semi-gloss paint, sanding in between each coat. The wood filler, paint, sanding and drying time is what caused the project to be more than just a weekend thing.