it is kind of cool to think about easy setup kites, but more when you just have to blow them, don't you think so?

Inflatable design is commonly seen in beach products that most of them are made in PVC sheets and a one way plastic air valve, the other ones are huge dummies that  need an electric fan so could be made of some fabrics and other materials; but they could be more useful in many things like this time to work as easy setup frame for the "kite".

The first and most important thing to know about inflatable design is the process to make them that is HF (High frequency) welding sometimes called RF welding; is a manufacturing process where two plastic parts of the same material (PVC generally) are welded together using an electromagnetic field (27,12 MHz).The objects that needs to be welded are clamped together between two metal electrodes and a high frequency voltage is supplied. 

As a result the molecules in the material starts to vibrate and heat up. Eventually the material will melt, and the force supplied by the electrode will melt (fuse) the two surfaces together. After cooling a permanent seam has been created. 

The resulting weld seam can be as strong - or even stronger - than the surrounding material. Here is were the first and "hard" to get material appear, find a HF machine. Depend of where you live could be more easy to find, my experience was to search the companies that make inflatables sounds logic, but is confusing when you find that most of them focus on the huge dummies that are made by sewing so be careful, is more easy to find on advertising factories that made products like clappers, balloons or even plastic tents, also this people have the valves, accessories and great inventory of electrodes shapes. 

There  are many parameters in the process (Electrical power, Pressure applied, Welding time, Cooling time, Materials involved, The specific geometries, Thickness, Area to be welded), so for a first time i suggest to know someone expert with this machines.

The same machine is used for weld the valve and accessories like plastic hangers and eyelets

The second thing in inflatable design come from the process; The sheets (the second material to get PVC sheets that comes in all colors and flavors) are putted one over another (like sewing) so you are restricted to work with 2D shapes but thanks to the air this 2 sheets into cool 3D shapes, even welding in different planes you can make almost everything in an inflatable version. As example look welding lines of a swim ring two sheets are welded in a form of two concentric circles 2D that inflated transform in an 3D torus.

Third tings based on experience: use rounds in your design, make big things and the most important iterate; the most cool and sometimes headache things about inflatables at the beginning, is that when you try something new you will never know what 3D shape is going to take by blowing air into.

So basically that it is talking about design, you need to plan everything, make many ideas, if you don't want to spend a lot on samples. 

The design of this kite is made using a vector program like Inkscape, Even free plans of kites could work just think about the inflatable zones, the valve and hangers; is just the front view of the kite traced with double line as easy follow guide for welding.

3D rendering in Creo parametric for good show (not necessary step)