As we are on the subject of head boards, here's an easier one to make which requires very little carpentry. None if you ask the lumber yard staff to cut the board for you.
We chose to make ours the width of the bed and added about 5 inches so it wouldn't look to narrow when the bed is made. I can't remember exactly how I decided on the height, but usually I consider things like, is it comfy when sitting up as well as lying down? I used chipboard as a base because we had some left over in the garage. You can use any board or even a wooden frame, the kind you buy in art stores and stretch canvases onto.
I added two layers of batting to make the board soft to lean against. This was stapled onto the back of the board and on top of the batting I stretched the fabric and stapled that on as well. I have to say I love my staple gun and I use it probably every or every other week on different projects. It's one of those tools you should have regardless of how small your tool box is.
To finish off I propped the head board against the wall, pushed the bed against it and it was ready. As simple as that!