Creating a Complex Custom Shape

Create a rectangle using rectangle shape tool.

Press Ctrl+T. Right Click and select Warp. Select "Flag" from the preset warp shapes. Adjust settings as shown.

Press Ctrl+T. Right click and select Flip Vertical and place on the other side.

Duplicate the path. Press Ctrl+T. Right click and select Flip Horizontal and place on the other side.

Similarly duplicate the path several times, scale down and place as shown.

Select and duplicate all the paths. Press Ctrl+T. Right click and select Flip Vertical and place on the other side.

Select all the path again. Duplicate them. Rotate 90°.

Select and duplicate all the paths again. Press Ctrl+T. Scale up and rotate as shown.

Enable "exclude overlapping shape areas" form the top bar.

Select the whole shape. Right click and select "Define custom shape". Named it "Shape 1".

Open custom shape palette. Select the shape.

You can use it as backdrop or background, logo etc. without repeating all the steps.