help with patch panel....

['68 Pieces]

Now i know, i know, another thread about patch panels, i see them all the time, im sure you guys get tired of hearing them, lol, but i need some help.

As we all know, our passenger side front fenders rot out, as do the radiator supports.

Well i finally broke down the other day and ordered some parts offline, ( yay, i broke the ice haha) So i got the replacement front fender "cup patch" if thats what u wanna call it.

Ok so if someone might be able to kinda walk me through it......... I have an air powered slitter wheel, a sawzawl, and a 90 amp 120V flux core wire welder and other misc tools..........

Now you cant just put the old one over top of it and trace it to cut the bad out...... so should i measure it with a soft tape and try and make the straightest line as possible?

Or im sure as some of us have done, just go out and learn for yourself? which i will probably end up doing.
guys im new to this so any info or PICS!! would be very helpful. Thank you