This is a design that I've seen around on the internet for a while. I'm sure the resemblance to a Klingon bat'leth is entirely coincidental.
Step 1: General dimensions
Step 2: Make a template
Step 3: Cut out the blank
Step 4: Smooth up and add the furniture
Put a notch in the centre of the beam to anchor the kite string.
Drill a pair of holes between the hand-holds. To one, attach a little carabiner so you can lock the kite line: when it's flying, pass the line through this crab to stop any more line paying out.
To the other, attach a loop and a big climbing carabiner. This will let you clip the whole thing to a belt or harness leaving your hands free to work the radio controls. CAUTION! If you've got a strong kite, you're light, or it's gusty, TAKE CARE because lifting kites can be brutes and being thrown around by one is a painful and expensive affair.