Grilling Surface for a DIY Barbecue
Almost all of the high heat sprays are not expected to last against direct flame exposure.

I have a outdoor fire pit/BBQ with plain rebar as the grill. Even though it does rust a bit, the exposed rebar is thick enough that it would be decades before I would need to replace it, and the baked on char/oils actually protect the metal quite a bit. The other option would be using stainless steel rods as the grill rack material, then there would be negligible amounts of corrosion.

If i had to remake the grate on my fire pit I would probably use 416 stainless steel rods like these http://amzn.to/2gV2DVD

Also, avoid anything that is chrome or zinc plated. When chrome or zinc gets burnt, they produce toxic byproducts. Just to be safe, I would avoid anything that is plated for your grill grates.