Scratch build roll cage

Any suggestions?
Is brass or plastic rods better.

Mark is probably your man but if you were accepting of less than perfection, I would say buy a partswork car of similar size and cut and shut it to fit perfectly, otherwise, brass rods.

As has been mentioned, its easier to use a cage from a similiar shaped car and modify to suit your base instead of startig from scratch.

For my 1/18 DS3, I converted a road car and used the cage from a C2 s1600. When im working on a Sunstar Mk2, i prefer to add to the existing cage using plastic rods instead of brass. For me its easier to cut, glue and bend plastic than brass.

How easy do the plastic rods bend?
Do they snap or is there a technique?

Depends on the plastic rods you get. Some are more like garden wire, so have a metal wire running through the middle so bend easily.

traditional plastic rods would snap, but when heated over a tealight candle they can be softened and bend to shape easily.