Here start making the outlines of the shape you want. You should also make some help lines to the plate. Then cut out the plate with a grinder or what you have.
You can se the center lines on the plates this will help you when you put these parts together. I use a rod that I bend to get the right shape on cutout on the top plate.
The plate is bent ower a small pipe and my knee. No Pro tools here needed.
Then tak in place. Remember the centerlines, now they come handy.
To prevent warping of the metall start in the middle then go outwards when welding. I use a TIG when I weld these parts easy and not so much grinding after welding.
When it comes to tricky parts like the sides of this piece I use cardboard to make a template.
I realy should take more pics but here the side is ready welded.
This is ready to be fitted on the fender. But it is a different story.