Actually the Mysims Ds version is a bit different from the wii version. In the wii you have to build a town but in the ds you'll be living in a resort town, were the goal is to bring new shop owners and money-spending tourists into town.
MySims will have 10 minigames you can compete in to earn cash for new items for your homebase. You can even head to a casino.
You can then take the money you earn from the minigames and purchase items for your home. Unlike in the Wii game, you will not be creating your house from scratch, but you will have many items that you can buy for the interior. As Sims move into town, they'll give you tasks to complete, once you do so, you'll earn new rewards. The more tourists that move in, the more stars your town will earn, and then more items will be available to buy.