Polyzosteria is a great genus of cockroach - they're big, often metallic-coloured, in some cases very colourful insects. They're diurnal and can be quite visible as they bask on tree-trunks and shrubs. P. limbata is a species that occurs around Sydney, though generally I believe it occurs more in the southern areas.
I had the opportunity to get personal with a female of this species for a few days and took it out into the garden today for some snaps. Overcast sky wasn't quite bright enough for good depth of field, but luckily the insect is pretty big (~45mm long).
I love the look of this roach, it may appear superficially drab, but it's got subtle bronze and iridescent colours, for example between abdominal plates and on the underside.