Belly Pan on LARGE SUV
 

How and where do i start making a belly pan

The biggest issue is the drive shaft... i don't want to damage it (RWD)

Start at the front.

Then the fronts of the tires.

The bellypan ultimately has to integrate with the splitter or air dam, wheel fairings, rear difusser and any side skirting. Everything needs attachment points.

Do I know whereof I speak? No, I'm being an NPC just saying the obvious things.

You could get inspired from here: https://www.youtube.com/watch?v=LxXCOT5ID20