It is lightweight and fits perfectly an Ocean Kayak Malibu II sit-on-top kayak. If you have a different kayak, only need to adjust the distance between holes in the frame to make it fit.
Enjoy it ;-)
Step 1: Materials
PVC pipes: 75 and 37 mm of diameter, about 1 meter of each one
2 screws with nut (M8x110mm) used as wheel axle
2 screws with nut (M6x80mm) to join the PVC pipes in a frame
Total cost of project: near 0 (just some cents to buy the screws)