Creating a magic item [closed]

I am creating a campaign, and I want to have a relic which allows the user to turn into a dragon for a certain amount of time. I have some ideas for rules, but I want some other suggestions.

The item will:

  1. Require attunement after each use.
  2. Require being level 10 to use it.

The idea is that at level 10, you can become a young dragon for 1 hour; at level 15 you can be a adult dragon for 1 hour, and at level 20 you can be an adult dragon for 6 hours.

It is a platinum dragon which is worth a very large amount, and is carved with draconic lettering.