Question about custom-made gowns

Hi! I’m currently looking into getting a custom made gown and I’m not sure how it works.

Do you usually meet with the designer first and ask them to sketch a design for you (may bayad po ba agad yun)? Or do you have to pay a downpayment first before they accommodate you or start working on anything?

Also, if you have any tips or things to look out for when working with a designer, super appreciate it! 🙏

TIA! 😊