From Bulbapedia, the community-driven Pokémon encyclopedia.
The Goldenrod Department Store is the largest store in Johto. It is located in south central Goldenrod City and contains many items not found in a traditional Poké Mart.
First Floor: Service Counter
Here, a receptionist welcomes customers.
Second Floor: Trainer's Market
This floor's slogan is "Your Travel Companion." It sells basic equipment and items Pokémon Trainers might need in their journeys.
Third Floor: Battle Connection
"For Victory Seekers" is the slogan of this floor. It sells temporary stat-enhancing items.
Fourth Floor: Medicine Box
A pharmacy selling permanent stat-enhancing items is located on this floor. Its slogan is "Let us pump up your Pokémon!" The items are the same in both Generation II and IV.
Fifth Floor: TM Corner
This floor is devoted to the sale of Technical Machines. The poster on the wall declares "Customize Your Pokémon!" Talking to the little girl on this floor unlocks the Mystery Gift option. There's also a man there who wants to trade a Drowzee for a Machop.
On Sundays, another shopkeeper comes and expands the stock of available TMs. She'll give out TM27 (Return) if the lead Pokémon in the player's party has high Happiness, or TM21 (Frustration) if it's low.
Sixth Floor: Tranquil Square
A picnic table and some vending machines are located on this floor. A sign implores customers to "Take a Break from Shopping". In Generation II this floor is called the Rooftop Square.
In addition to the vending machines, in Generation IV there is a raffle that can be entered for 300, with a chance to win either a Berry, a certain type of Poké Ball, or a TM (selection changes depending on the day of the week).
Lottery prizes by day:
This is the uppermost floor in Gold and Silver as well as in HeartGold and SoulSilver; in Pokémon Crystal, however, there is an additional flight of stairs leading up to an additional floor.
A floor exclusive to Pokémon Crystal, the rooftop cannot be accessed by the elevator; instead the player must travel up the final flight of stairs. Some binoculars let spectators see things far away. Some people go up to the roof top to take a break from shopping. There are also some vending machines selling tiny Pokémon dolls. Players cannot buy anything from the doll vending machines, because there are none left. However, there is an occasional Rooftop Sale, which Camper Todd from the Pokégear will call about.
The basement is only accessible from the Department Store via the elevator.
A team of workers and a Machoke are moving boxes around. People get told off by the worker for going down and distracting them. This is one of the endpoints of the Goldenrod Tunnel. Every time the player enters the area, the boxes will be moved in various places, allowing access to items that are on the ground in blocked rooms.
In HeartGold and SoulSilver, talking to the workers will cause each Machoke to move a box, allowing access to each blocked room and the items inside them, with no need to leave and reenter the area.