Flattening solid object

Hello everyone!

I am struggling with finding the right method how to generate flattened solid from curved one.

The problem is how to find a right length of sheet material (5mm plywood) since flattening each face individually doesnt make a right result + one edge of the solid is cut under the angle.

I have attached rhino file of solid I am willing to flatten so I could cut the sheet before bending it.