Here is what I had made last winter:
Not a bad grill block but I did not like having the logo open (it stuck out too far to go over though). It came off in about 3 seconds (nice pop with a screwdriver).
First thing I did was to make a cardboard template. You can also start with paper, but my shape was not that complex so I went with cardboard.
I took an old box and cut it to the height I wanted (top to bottom), then I taped it up on the car. Next I marked the rough edge (out about 1/2 an inch to give me room to fine tune the edge). Once that was done I marked the edge with a pencil and cut the exact edge I wanted. Repeat on the other side. I waited to do the other side so if I screwed up my cut I could just move the cardboard over and inch and try over.
Next place your template on your grill block material. I used some galvanized steel (same as I used for my wheel skirts). If sheet steel is not handy try colorplast.
Trace your template onto the grill block material (if using metal mark the shape and make a 3/8" larger line). Cut the line (use the outer one with metal). With colorplast skip this next step.
If using sheet metal bend along the traced line (inner one). Use vice grips to bend on the line up past a right angle. Then hammer over the tabs (pound it flat).
This will make the edge rounded and not sharp (does not scratch paint or cut your hand when reaching for the hood release).
Now check your fit on the car:
If you like the results you can attach it (if not go back and fix it). I used self tapping sheet screws to hold mine on (screwed into the holes that were filled in on the back).
Other ways of attachment that worked for me:
Zip ties, nice for testing, not so good of looks.
Flat headed bolts (see the first picture).
Paint as desired.
I ran out of primer and silver paint so I will post pictures when it is done.