I’ve written two things to help. You can find them at GitHub - mainiacjoe/Vault_Contributions.
There is a Python script and a custom palette designed to work with piskelapp.com. You can draw your map in a pixel editor and covert it into map glyph syntax.
There is also a very thorough beginner’s guide that walks you through making an arrival vault and submitting it to the Devs via GitHub.
Please take a look at these, and hopefully you will be contributing vaults to Crawl. Let me tell you, when you run into your own vault in a game, it’s a great feeling!