From Nookipedia, the Animal Crossing wiki
T&T Emporium (まめつぶデパート Mametsubu Depāto?, Mametsubu Department Store) is a new store in Animal Crossing: New Leaf, owned by Timmy and Tommy. T&T Emporium is the fifth and final store expansion of Timmy and Tommy's stores, after being upgraded from T.I.Y. The expansion adds another two stories to the building, along with a huge selection of items. A fifth store upgrade is new to the Animal Crossing series, with the previous games having only four of them. T&T Emporium is similar to Nookington's, except that Tommy and Leif are on the first floor, Timmy is on the second floor, and there is an added third floor where Gracie is.
The first floor of the store holds main products, including tools, stationery, medicine, and fortune cookies, along with products pertaining to gardening. The second store contains several furniture items. The third floor is home to GracieGrace.
To upgrade from T.I.Y. into T&T Emporium, the following prerequisites must first be met: