Walkthrough

1. Gather the materials and Pokemon needed to build the second floor of the building. You need 25 Concrete, 10 Glass, 5 Pokemetal, 10 Iron Ingots, and 6 Pokemon to help out.
2. Gather materials and Pokemon to build the third floor of the building. You need 25 Concrete, 10 Glass, 10 Shiny Stones, and 10 Copper Ingots.
3. Go to Rocky Ridges and have Chef Dente follow you to help build the third floor of the building.
4. Gather materials and Pokemon to build the fourth floor of the building. You need 40 Concrete, 15 Glass, 10 Paper, 10 Bricks, and 20 Lumber. You will need 15 Pokemon to help build the fourth floor.
5. Go to Bleak Beach and ask for Peakychu's help. Have him follow you to Sparkling Skylands.
6. To obtain the Paper, you need to build the Professor's Apprentice Program habitat. This requires 1 Whiteboard, 1 Jumbled Cords, 1 Table, and 1 Laptop.
7. Collect the Jumbled Cords and Whiteboard on the cliff located east of the building entrance. Collect the Laptop on the first floor of the building.
8. Place the Professor's Apprentice Program habitat in front of the building entrance and wait for a few minutes in order for Metang to appear. Talk to Metang to have him convert the Wastepaper into Paper. You can find Wastepaper scattered all over the area.
9. After completing the fourth floor of the building, take the elevator inside to reach the rooftop. Examine the Master Ball to raise your Trainer Rank to Master.
10. After examining the Master Ball, return to the entrance of the building and speak with Professor Tangrowth to complete the important request.

Walkthrough source: Game8.