How to draw a new shape through existing shape edges?

I drew a shape like picture one.
Now I want to draw a new shape above, fitting the edge of existing shape,
so that I can extrude them separately,
but I don’t want to draw the edge of existing shape again.
What is the better way to draw the new shape?
Thank you!

Hi Womicry

There is a lots of ways how you can do it.
I’m using this one.
Please see attached file
New shape solution.3dm (644.2 KB)

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