Design Options
Laurie's objective with this headboard was to cover the large upholstered panel with a grid of wood strips to create the illusion of multiple, small panels surrounded by wood trim. She described the wood strips to resemble muntins, which are wood strips that separate panes of glass in a window sash. Today, muntins are often purely decorative items that are set on top of large panes of glass to give the appearance of traditional divided windows. This headboard is constructed the same, somewhat deceptive, way.
The frame and grid assembly is an optional feature of the headboard. You might be just as happy attaching the padded and upholstered panel directly to the wall, perhaps using attractive screws with trim washers or one-piece washer-head screws. Just be certain that your screws go through the wall and well into the studs.
If you like the grid idea, but would rather stay away from the somewhat tricky woodworking needed to create the half-lap joinery, consider using a different material. You could build the frame, as described below, and then fish some cable, twine or strips of fabric through holes drilled in the sides of the frame to create a functional grid-like appearance.
Plan the Size
The upholstered panel is the primary visual element of the headboard. It consists of a piece of plywood covered with batting and fabric. The only real decisions you need to make are how big to make the panel and what kind and color of fabric to use.
The width of the panel obviously depends on the size of your bed. You may want to measure your mattress to be sure, but mattress sizes are pretty standardized these days. Kings are 76 inches wide, queens 60 inches and doubles 54 inches. For a typical bed, make the panel the same width as the mattress. That means you should plan to cut the plywood a bit smaller than this dimension, as the fabric and batting will be wrapped around the edges to create the finished width.
The height of the panel is largely, but not entirely, a design choice. The headboard that Amy Wynn built for Laurie was a full 8 feet high, which works fine in a room with very high ceilings. Many people, however, are faced with ceilings that are 8 feet high, and would be well advised to keep the headboard a foot or two shorter. Try hanging a sheet on the wall at different heights to give you a sense of how different sizes would look on your wall.