Green’s Dictionary of Slang

1. (Aus.) assembly, ‘get-together’.

1885		Bulletin (Sydney) 31 Jan. 14/3: [O]ur Anniversary Day racing roll-up is over, and the duly phlebotomised general public has a chance to sit down in a cool spot, and philosophise over the uncertainty of things in general.
1890		‘Rolf Boldrewood’ Miner’s Right 308: Making as much noise as if you’d hired the bell-man for a roll-up.
1904		Sun. Times (Perth) 17 Jan. 2/2: A big roll-up is expected at Belmont Park on Saturday.
1912		Bulletin (Sydney) 8 Aug. 38/3: There was a large roll-up at the Orchestral Society’s concert, on Tuesday.

2. (Aus.) in spec. use, an unofficial trial, held in the goldfields.

1890		‘Rolf Boldrewood’ Miner’s Right 185: At the Warraluen and other gold towns, time after time the ominous words ‘roll up’ had sounded forth, generally followed by the gathering of a mighty crowd.
1914		Bulletin (Sydney) 29 Oct. 13/2: There are many spots in the wide Outback where the Warden’s law fizzles out and the diggers’ law puts a half-Nelson on the malefactor. The ‘roll-up’ of the prospectors at gold-rushes, or the ‘muck-heap trials’ of the opal-gougers, gives an accused a fair run for his money. [...] We stood up one of the ‘Ragged Thirteen’ at a ‘roll-up’ (charge of murder) at Mt. Ida.

3. (US prison) of an inmate, the act of leaving the prison, whether temporarily (for a court appearance) or permanently (after completing a sentence or moving to a new prison).

1986		J. Ellroy Suicide Hill 6: ‘Homeboy here is going to trusty classification. [...] The other guys are roll-up’s for work furlough and weekend release’.
1999		E. Bunker Mr Blue 287: The parole officer had not yet put the detainer on me when the roll up was called.