To quickly get feedback on the design you can create a quick mockup of the design.
If there are crucial questions to cover first you can ask the user those questions.
Otherwise you should go straight into create a mockup. The mockups can be created in a temporary system directory, or a mockup/ subdirectory of the project, but the former is preferred. On iterations - for learning purposes you might version them eg. mockup-v1.html. In later development you might reference them so that the next agents are aware of the mockups/ current mockup.
Once it's done tell the user how to open the mockup and await feedback - or better - use a terminal command to open it for them from the terminal.