it's not an external roll cage...it's a ladder rack...
There are regulations about how far things can protrude from the body but being an exo you want to keep it close.
my $0.02.....don't bother with exo in vic. a nice solid 4 point internal is going to give you heaps better protection and will keep the weight down and centre of gravity low.. If you are going to do it, just protect the panels that count...roofline, windscreen surround. Get some nice rubber wheel arch flares and everything will bounce off them
Otherwise go speak to a company like brown davis who's job is to build ROPS for racing through to mining applications they will point you in the right direction.