convert object made with 3d lines into a solid

[turboCAD]

Hello everybody and thank you for having made this site where people can share ideas and and help others improve their Autocad skills.
I drew a 3d shape using 3dpoly and I want to convert that drawing,which is now only a 3d sketch, into a solid.I have attached a picture of the lines sketch
sulita.jpg.

Thank you!

[ReMark]

Are the 3dpolylines open or closed?

[turboCAD]

Strangely, it says they are NOT closed.

[ReMark]

Why not just create the object as a solid to begin with?

[turboCAD]

the creation process for this object went as follows: I drew the surrounding lines and a space was left between the lines; I have to fill that space perfectly with an object of dimensions that are not standard (the angles are odd, the dimensions of the lines are not round numbers), the base of the pyramid is a rhombus rather than a square...But most of all, I want to be able to create a 3d object out of a selection of lines that describe/outline/border that object.
Precision is crucial, this is the bottom line.

[turboCAD]

it basically consists of two pyramids with a rhombus shaped base and different heights

[ReMark]

Great explanation but I did not understand a word of it.

If you have a closed 3dpolyline then you can convert it to a surface. Surfaces can be thickened. If you have enough surfaces to create a water-tight structure then that, in turn, can be converted to a solid (AutoCAD 2012 and higher) via the SURFSCULPT command. I just tested the method and it works. I am currently running 2012.

[turboCAD]

If I were to extrude all surfaces and keep their common points it may work.
Is there a way to do that, extrude all surfaces and keep the volume that is common to all?

[ReMark]

You don't extrude the surfaces you thicken them with the...THICKEN command.

[turboCAD]

have a little more patience with me,please, I don't know how to create a surface from 3dpolylines. I would be grateful it you explained how to do it.
thank you, ReMark!