Freeze branding irons and hot branding irons are made from different materials. Either heavy copper or brass makes up the brand of a freeze brand and I think it is either iron or steel that is the hot brand (or the electric ones work well if you have power). If you plan on making your own hot brand make sure to take into account the heat and create "vents" or spaces so your brand doesn't end up a big burnt blotch. Personally, I wouldn't even try the freeze brand.
I assume you are already a brand owner...if not you need to talk to your state livestock department to see what is needed to own a brand. Some states don't recognize freeze brands on cattle for ownership. I believe calf brands (hot) are supposed to be 3" and cow brands are to be 4" (in MT, your state may differ).