Why I build my Airspeeder? Well, I started looking through brickset's star wars set collection, figuring that if Lego had not made a lego model of it, it would obviously be too obscure. With the notable exception of Padme's shuttle. But looking at you, Skyhopper!
Anyway, I selected a few I liked and were somewhat non-obvious, being the Sand crawler, the Pirate Tank, and the Koro-2 All environment Airspeeder.
I actually found there is another intriguing sand crawler design:
But I abandoned the idea because I could think of a new shape, and frankly was a bit scared of how big the model would have to be.
I did sketches of all the models, but the airspeeder was the first where I could evolve the shape and found it would look cool with large, visible engines.
I also found that the original Lego model (in set ) was a really nice Lego spaceship. But it looks pretty terrible if you compare it to the actual ship in the movie.