Walkthrough

1. For completing this request, you can get Withered Wasteland Pokemon Center as a reward.
2. Withered Wasteland Walkthrough
3. For completing this request, you can get Bleak Beach Pokemon Center as a reward.
4. Bleak Beach Walkthrough
5. Most of the materials required to rebuild the Pokemon Center are also easily available in the overworld. You can use Rock Smash on rusted metals to get Iron Ore, Seaglass Fragments are littered across Bleak Beach, and Twine can also be obtained by using Cut on stray fabrics.
6. For completing this request, you can get Rocky Ridges Pokemon Center as a reward.
7. Rocky Ridges Walkthrough
8. For completing this request, you can get Sparkling Skylands Pokemon Center as a reward.
9. Sparkling Skylands Walkthrough
10. Raise your Environment Level to 3 to unlock and purchase the center's building kit from the shop. It costs 1000 Life Coins. ► How to Raise Environment Level
11. Next, gather 20 Lumber, 20 Stones, 10 Leaves, and 10 Vine Ropes. These are all the materials required to build the Pokemon Center.
12. Befriend various Pokemon like Scyther for more lumber, and to get the Cut skill, which you can use to cut down trees for leaves and wood, as well as vines for vine ropes.
13. You'll need Onix for the Buldoze specialty to get rid of the rubble. Complete the Yawn Up a Storm request to rescue them.
14. Once all of the requirements are met, submit all of the materials and bring all the required Pokemon to the site and begin construction.
15. Wait for the construction to finish. A good tip is to advance the time on your system settings to instantly finish the construction.
16. To start, raise the environment level of Bleak Beach to Level 3. The Pokemon Center Kit will not be available until you reach this level, so make sure to keep building habitats, befriending pokemon, and doing other requests first to reach this level.
17. Create a yellow tall grass habitat to recruit a Spinarak or Ariados. This is the best way to get Twine, which you'll need as part of the materials for the Pokemon Center. Collect ten for the Pokemon Center.
18. Progress Meowth's requests, specifically Clean up the Mud and Flowers in the Planter. These quests allow you to befriend Torchic and Piplup, which you'll need to get the other materials.
19. Once you have Piplup, clean all the dirty muck on the beach. Underneath these are Seaglass Fragments. Get ten of these for the Pokemon Center.
20. Once you have Torchic, head back to Withered Wasteland and go to the cave where you rescued Onix. Smash the surroundings to get Squishy Clay. | | Get at least 15 of these to produce 30 Bricks for the Pokemon Center, then give them to Torchic to process.
21. Piplup will eventually ask for a Shower too, which requires Iron Ore. Make a Trash Collection Site to befriend Trubbish. With them around, you can collect trash and convert it into Iron Ore for the Pokemon Center. | | Give Trubbish at least four nonburnable garbage to get 8 Iron Ore. Use 5 for the Pokemon Center, while the others are for Piplup's request.
22. Once you've gathered all the materials, invite all the pokemon to start the construction. The specialties required for this are Water, Bulldoze, and Build. | | If you haven't befriended anyone in Bleak Beach with these specialties, you can return to Withered Wasteland and invite the pokemon you have there instead.
23. As with other Pokemon Centers, raise your environment level to three to be able to purchase the Pokemon Center Kit. Continue progressing through the story in Rocky Ridges and you should be able to reach this level immediately.
24. Rescue Chef Dente in the building above by learning how to cook and bake. This also unlocks Torkoal and Dartrix.
25. Chef Dente will then ask you for a frying pan, which requires a Copper Ingot. This requires access to the Smelting Furnace, triggering Machoke's Cut Down That Fence request.
26. After completing the quest, head deeper into the mine and you'll find the Smelting Furnace. You'll have all the items required for the Digging and Burning habitat here, so just rearrange them to form the habitat. Magmar will appear after.
27. You can now use the Smelting Furnace to make Iron Ingots and Copper Ingots. You need 25 of each for the Pokemon Center.
28. Copper Ore can be found on rocky blocks, while Iron Ore can be found from rusting parts or by asking Trubbish to make them from non-burnable garbage.
29. The Crystal Fragments can be found in the same mine. Head deeper into the magma area and take a right. Destroy the blocked path and follow it to the end to reach the room with Crystal Fragments. Use Rock Smash on the light blue stones to get them. Collect five for the request.
30. Collect Stones along the way for the last material, and you also need 25 for the request.
31. Once all the materials are complete, you can now start the construction to rebuild the Pokemon Center.
32. Raise the environment level to three to be able to purchase the Pokemon Center Kit. Do this by befriending more Pokemon and making more habitats for them.
33. First on the list of materials is Pokemetals. You can find these at the far east of Sparkling Skylands. Befriend Gardevoir and progress their quest, and they will lead you to an area filled with Pokemetal blocks. Power up your Rock Smash to break these and gather 25 for the request.
34. For the glass, head back to Rocky Ridges and destroy any volcanic ash you can find. Use these to make glass. Other blocks, such as sand and sandstone, can also be used. Collect 25 of these as well.
35. For the gold ingots, enter the room where you can find DJ Rotom. Go deeper into the cave to reach an area with Gold Blocks. Power up Rock Smash again to destroy these, and gather 25 for the Pokemon Center.
36. Finally, progress the Make Concrete request to make concrete. You will need to meet Tinkmaster and befriend Conkeldurr, and once you have them, you will learn how to make concrete. You will need 25 of these as well.
37. After gathering all the materials, assemble your team and combine the materials to start rebuilding. The Pokemon Center should be complete the next day.

Walkthrough source: Game8.