Scaffold bar: made from any old shyte and rat droppings dug out of a chinese sh*thole. Featuring a large, weak seam down one side of the tube.
CDS: Made from, errrrr cold, drawn steel, to proper specification.
Using scaf bar for cages is a VERY bad idea, never mind the weight implications. Don't do it. You don't know how it will deform or snap.
Plus cage tubing should be mandrel bent, really
HTHs
The price of Custom Cages (or any of the other start-ups from ex-CC employees) means you are probably better off just buying a kit. Think about where you're cross-bracing it though - a vertical brace may not work if you're 6'ish due to the size of the passenger compartment.