you have to unlock all the worlds and help everybody out in them. once you have done that, you will unlock your own little island to build whatever you want on it! re-visit all the other islands and see if they need more help. once nobody needs your help anymore, you're finished!
you have to finish the electisit scroll.
Wii console.
cutopia
Treasure Finder!
prospect
no
do all the missions
trevor island
the uncharted isle
YoU hAvE tO cOmPlEtE tHe RoCkEt ReEf
the cowboy island
you have to finish helping all the islands and then you will get an island for yourself where you can build whatever you want and do whatever you want! this is when you know you've won the game!