Galactic Civilizations 3 developer Stardock has announced a Spaceship Builder contest with a top prize of $1,000 and the chance for eight fan-made ships to appear in the game.
You can submit your designs from now until November 16th, while the eight finalists will be voted for by the community between November 19th and December 9th.
While the prize is in US dollars, anyone is allowed to enter so long as they're legally eligable within their own jurisdictions. Stardock hasn't placed a cap on the number of submissions you can make, but they do suggest you limit yourself to no more than five.
You can submit your ships here, while the competition's rules are explained on this webpage.
Galactic Civilizations 3 is currently in beta, and Stardock expects to launch the game in early 2015.