MBK 1-Skewer Barn Door
You might already have some of the simple tools and materials required. Anything you don't have is easily bought.
If not exactly what I used, then at least something pretty similar!
These instructions on how to make a Barn Door kite might look a bit long, but each step is quite simple to do.
Just steadily work your way through from top to bottom, skimming over any detail that you don't need.
At 29cm (11 1/2") from tip to tip, the MBK 1-Skewer Barn Door Kite is a rather small Barn Door, with dihedral and simple 1-leg bridle.
The little Barn Door is a fine light to moderate wind flier.
As a bonus, these instructions also show you how to string several of these kites together in a kite train!