There are 9 different items to craft from Gobber, 3 helmets, 3 shields, and 3 armor pieces. All 9 take different amounts of the normal stone pick ups (Red, Blue and Purple stone) that you will find destroying stuff and in chests. You can complete this anytime you have the materials after Gobber’s wares are open to you. **You have until the end of the dungeon in the third area to complete this.** You can leave any non boss battle area and return outside by holding “Y” (Destroying most things I could along the way and opening the majority of the chests I was short about 1500 blue stone for my last two items. The last dungeon gives lots of materials in chests but will reset all dungeon puzzles if you exit to go craft. I chose to return to the second area to destroy and grind. Took about 3 runs of that to get what I needed so it might be easier to just reset and leave the third dungeon when you have what you need as long as you don’t finish the dungeon.)
**According to DopiestEarth8 it seems to be now possible to go back into your game to continue to upgrade after the final boss, I do not own a copy of the game anymore and am unable to verify or deny so proceed at your own risk on whether or not to finish upgrading before the final boss**