This was really the easiest one, I came across these metal flowers at a Hardware store. I think it is actually meant for gates and fences, but it really is a great shape for a besagew. And as for attaching it, a leather strap . You will attach the besagew at the shoulder, so measure from your shoulder to the center of your besagew when you hold the besagew where you need to position it. Punch one hole at the top of the strap and two holes at the bottom an inch apart. You then Rivet the strap to the flower through the second to last hole, because the last hole is to lace the besagew to your chest (as an eye witness I can say that if you ever run in armour while not wearing a helmet, your besagews will hit you in the face if they are not laced down)
If you don’t like the flower design and want to go with something else, the internet has a few stores offering round steel plates that are slightly dished for a few dollars a piece.
The tools used for this easy little project are a hammer, a sledge hammer as an anvil, a sharp knife and a hole punch for the leather. the materials are not more than a pair of steel flowers, a pair of rivets and washers, and straps made from leather scraps.