Make you own Island

  As the population booms, overcrowding is becoming an ever increasing problem. So, why can't we make our own land? Now I've seen this done, I know that they did this in Japan for a new airport... I think. Can't they do it on a much larger scale, to make a land-mass? It would be a big project and take a long time, but I don't see why It can't be done, I think we have to consider this option before we think about moving to mars!