As someone who has tried to help out an inspiring creator like you before, I have a bit of advice. First, if you're lost in thought or looking for inspiration, then having an artist make the story and manga for you is not the answer. If you give the artist more freedom on forming your story then it is no longer your story, its the artist's story. I recommend only searching out for an artist after you have the premise for your story down. If your looking for inspiration or that spark of creativity, trying watching animes or movies that are close to what you're trying to make, listen to music that sets the tone of the world your imagining, and as what was already mentioned before, try asking an artist to draw you a scenic design of your characters so you can have a clear idea on how they would look.
However, As a manga artist myself, most aren't going to want to make an entire manga for you for free. Making and designing a well-created manga takes a lot more effort than you can imagine, especially if you don't know how long the manga is going to last. So, I recommend trying to take it slow and build up your creativity before asking for a full-time artist to help out. Hope this helps in any way.
