This is how I did one. Nothing special obviously, I just dropped some decorative items on top of it.
I have seen a few examples of using multiples of the large forges in both directions, and chopping them (I think Sarsmi may have posted a tutorial for that at some point), to form a sort of "plus" shaped mega grill/forge. I am not sure you can still do this though, with the changes that were made to gozas and add-ons a while back.
I have also seen some really cute small forge grills and "habachi" style grills made with wooden boxes and other bits of items, and some great item built fire pits.
-Skylark