How to create a flat 3D shape/a flat plate, but with more than 4 corners?

[Soulbrother]

Hi,
I know how to create a wall and use this as a 3D form (shape).
But I would need a more complex shape, easy enough to draw as the ground ("floor-shape of a room"), but I wonder if it would be possible to use a room´s "floor-shape" as a 3D export, to create a 3D shape.

Or is there another tool to be able to create a "poly-shape"?

Thanks for all hints

[Mike53]

The room tool is the right idea, create it on a level other than ground floor, that way you will be able to set and/or adjust its depth. You can freehand the room or use walls, set at maybe 2mm wide and 2mm high to draw the shape you require.