For this Barn-Door, you need long lengths of 5mm (3/16") wooden dowel.
It is easily cut to the lengths required with a small cheap hack-saw.
Note: The length of bought dowel can be somewhat inaccurate. So if you have bought 2.4 meter lengths of dowel, you might have a couple of centimeters less than you bargained for! Hence I cut my 120cm spars from 1.8 meter lengths of dowel.
Now there's a little work to be done on the horizontal spar. Use 20 pound flying line if you have some, otherwise just use some of your 50 pound flying line. With this kite laying on the floor, each tip of the horizontal spar will be 0.08DL (9.6cm, 3 3/4") above the floor.
The remaining steps...
After the bridle has been made up, one line connects to where the spars cross, with a Lark's Head knot. This is shown in close-up, in the bottom photo.
As mentioned earlier, there's more kite-making on this site than you can poke a stick at :-)
Want to know the most convenient way of using it all?
The Big MBK E-book Bundle is a collection of downloads - printable PDF files which provide step-by-step instructions for many kites large and small...
Every kite in every MBK series.