An example in C is provide in the RKM (Rom Kernal Manuals) for Kickstart 1.3, it can be found on
http://aminet.net/package/dev/src/RKMCompanion. Hope that helps
. The code use a gfx bitmap for RoundRects. You will find it extracted in the Intuition/ drawer, I can't remember what drawer in the Intuition folder I'm guessing the Requestors
I don't ever recall using such a requester as well.