Could Gandalf not have made his own One Ring?
I know that he wouldn't have wanted it, but how would it have worked exactly?

I was thinking...

Gandalf, being one of the Istari, had access to the One Ring when it was kept in Sauron's fortress. At this point the ring was not yet 'complete'. Maybe he didn't notice it's power at this point or didn't want to risk contamination, or maybe he realized that it couldably be used by someone else for evil, even by him, though it was intended for Sauron. He had many years toably
Can elves make more One Rings? -- Aragorn23

There is of lore regarding the One Ring and its creation:

1. Only Sauron could make an Elven-ring with the power of the One in it. There is mentioned in The Silmarillion that even the Valar had a great deal of trouble creating their rings since they were not in the same league as Sauron. No one but Sauron could create a Ring of Power like the One Ring.
2. No Elf, Dwarf, or Man could make a Ring of Power for themselves