Firstly go into nooks shop and buy any item thats over 3000 bells. after you have done so, send it in a letter to your nearest neighbour you have. If you don't know how to send it in a letter basicaly you write a letter and drag the present onto it then send it away at the post office. Next get the bus into your town and go into gracie gracie's shop. Buy another item costing 4000+ Go back to your house and you will have three floors - a basement,the floor you started with and onother one on top. Also with this cheat you get a magic tunnel at the back of your house which you can enter by buying a door costing 1500 bells at nooks or 3000 at gracie gracie. Place it anywhere on your wall and the tunnel will appear.