He encontrado esto:
The Museum Renovation is a Main Street upgrade and costs 198,000 Bells. It is requested by Blathers once the player has spoken to him on 14 different days and donated at least 20 items, with at least one item in each of the four exhibit categories (fish, insects, fossils, and art).
The renovation opens up a second floor in the Museum that features a gift shop which sells Silver Tools and various museum related items, a locker not unlike the one found in the Train Station, and four 8 by 8 exhibit rooms run by Celeste which cost 10,000 Bells each to open. The player may use these rooms to display their own exhibits.
Supongo que lo que nos falta son los días de espera...