How do i build a Professional Parabolic Solar Cooker

[Greenshield]

Hi , I m 22 Year old guy wanting to start a solar company , i wanna build this cooker but i can't understand the assembly

I m looking to build something like this which looks professional and has light weight , Does anyone know how to construct something like this
I m unable to understand why are there screws in the middle of reflective sheet( see red circles) when there is no frame to screw that into? I get the mainframe screw part which is pretty simple
And How to calculate at the amount of reflective sheet required for specific diameter that when cut in triangular shape it fits perfectly and leaves no gaps
Please help!