This was a hit right in the corner of quarter panel.
I went to junk yard and sourced quarter panel, taillight, bumper cover and mirror.
It's very important to cut patch panel right the first time, you can't weld additional metal on it once it's cut off. Start out by drilling out all the spot welds. Once you remove damaged section the underlying metal can be straightened with rubber mallet.
You want to cut patch panel slightly bigger cause it will overlap over the edge of existing panel that you will be welding onto.
You want to double and triple check all the gaps by installing donor parts (ie bumper cover, tail light, decklid to quarter panel gap.
Once you're happy with gaps you want to tack quarter panel in a few spots so it won't move out of alignment.
You want to protect glass/interior from sparks. A cheap fiberglass blanket works well but be careful of fiberglass splinters
After all of the welding is complete I grind it down, you want to cool off panel and weld on lowest heat setting, you want to minimize panel warping.
After all welds are ground down I put body filler and sand it down. Next coat of body filler is applied slightly farther and so on.
Once body filler work is done I mask entire car (it's important to do so, overspray travels everywhere and you sure don't want to try to clean it off of entire car.)
You can buy masking plastic from body shop supply store at $5 and it will cover entire car.
I use 2K high build primer and lay on 3-4 full wet coats. It's best to let it dry overnight, it sands much better once it dries
thoroughly.
You might find imperfections while sanding primer ie little pinholes or slight low spots etc. I use Glazing putty, it goes over primer and dries fast/sands easy. Afterwards I'll put another couple coats of 2K high build primer over entire panel.
It is important to use sanding blocks, not your hand. Especially on body lines (this car has plenty of them)
I finish sand primer with 600 wet.
After primer work is complete I take car outside and thoroughly wash it, you want to remove as much dirt/dust from car as you don't want it in the air once you start painting. Next step is masking. I throw plastic bag over entire car except for panel that I will be painting. You want to use 12" or more masking paper around your area to be painted. Reason is, paint and clear coat overspray sticks to paper not the plastic bag. You don't want dry overspray landing into your fresh paint as you're making a pass with your gun, that air will lift overspray from plastic but not from paper.
They make "blending agent" for paint (base coat) and blending solvent for clear coat. For each coat you simply step out father onto the panel you're blending into, this way you won't see blend edge. If done properly you won't see difference at all.
This is where higher end paint makes all the difference. A pint of this paint was $120 but well worth it in the end as it matched car color perfectly. For the clear coat I went with cheper clear $22/quart+8oz can of hardener $16.
After this paint job dried overnight I buffed it with my Meguiar's kit, detailed car and started assembling it.
) Then refinish the area with a rattle can of high quality Tremclad, a little buffing and you just scammed the customer out of their hard earned money. Isn't that how it's done. I tell ya, if your into the fixin stuff right and giving value for dollar your a bloody dinosaur. Like they say, do unto others then take a holiday down south. 
Wow, just wow!