Ive looked into these before. Its built around a Jetski base (the running gear) and at the time they were using ex militry jet canopies and a fibre galss body.
They were hoping to try and get some sort of racing competition working (the idea was meant to be like the red bull air races but in the water - not a clue if they got it off the ground).
It would take a while (and prob cost more in the long run with all the tweaking etc) but i dont think it would be to hard to build (in theory).
Seems things got expensive since i checked all this out ... the opposite is the flying hovercraft