So without more intro bring it on.
Materials and tools to have:
PVC sheets, at least 5 meters for iterate any color, thinner better for the weight, but easy to broke.
High frequency machine or know someone had one.
Plastic PVC valves.
Plastic PVC eyelets (this one is an option for attach for the string)
Plastic PVC hangers (this one is another option for attach for the string, but more creative options could be done)
Inkscape for the drawings
Kite reel off course
Step 1: Know the Process for Make Inflatables
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
More details and videos of how it works here:http://www.fiabmachines.com/
A DIY option is glue but apply it very well between sheets.
Step 2: Design It
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.
some 3d rendering in Creo parametric for good show (not necessary step)
Step 3: Fabricate or Find Someone Do for You
The first thing to weld is the one way valve that use a sometimes called electrode (cylinder) or mold or die. Also is good to weld eyelets ir hangers for the rope. (first prototypes i tried many places for test different configurations)
HF welding process uses" electrodes" that are good electric conductors as copper or aluminium, for samples thick wires are used for so any curve could be made for achieve almost any design, remember the rounds.
Needs expertise to made a proper continuous weld that doesn't allow air come in or out.
Step 4: Try It
Same advises as other kites don't forget safety, speed wind, string adjustment and someone help never enough.