Polythene sheeting, the type you buy at a garden shop that's about 125 μm thick, is great for kite making. It comes in black and clear, the black is boring but the clear can be a bit hard to photograph against the sky.
This kite is a cross between a sled and a para foil. I based it on plans found here. The instructions are in French but fairly easy to follow with the help of a dictionary or google translate if you don't read French.
I combined the pattern for the Dos (back) and the tubes into one piece. Draw them up directly onto the polythene with a felt pen. If you're likely to make more than one it might be worth making a paper pattern. Draw the seam lines onto the sheet. Then cut the two pieces out of the polythene and sew them together with four lines of machine stitching.
The polythene is pretty slippery on the sewing machine. Use a long stitch length and keep one hand behind the needle and one in front feeding the material through.
I reinforced the front edge with some left over end lengths of line trimmer line. This is nylon line about 2.5 mm in diameter used in line trimmer for cutting weeds. Pick some up at the garden shop when you get the polythene if you haven' got any sitting about. I stuck the line to the front edges with squares of duct tape. These didn't hold all that well so I stapled through each square to hold it in place.
You'll also need a drogue, mine is a truncated cone, about 400 mm long, top circumference 500 mm, bottom circumference 300 mm. Sew two sections together and add line trimmer line along the leading edge as for the main kite.
That's it. No spars, or dowels. It flies fairly well in most winds. I intend to use it to do some kite photography. Maybe with some first person view camera gear.