How can I get the second floor for my town's museum in ACNL?
Donate to the museum 1 item of every category. In one category put in 20 or more bugs, fish, dino bones, or paintings. Talk to blathers every night past 7:00 PM. After 2 weeks Blathers should mention about a museum extension. You must be the mayor when talking to him. You may be unlucky and not have him talk about it for 2 or 3 years. I actually got mine in the 2 weeks. I hope yours comes soon too! :D