These are the general rules for Andra Cages, not sure if they've changed recently though...

ROLL BARS / CAGES
• Street registered open cars between 11.00 and 12.99 (1/4 mile)/7.00 and
8.50 (1/8 mile).
Single rollover hoop covering the full width of the drivers compartment with two backstays and a side intrusion bar of welded construction constructed to ANDRA requirements as a minimum. (Figure 1). Utilities may use a four point roll cage with intrusion bars / diagonals on both sides. Roll cages fabricated from aluminium will be permitted in sedans with fixed steel roofs slower than 11.00 seconds (1/4 mile)/7.00 (1/8 mile), where the original monocoque construction of the vehicle is unaltered.

• All other sedans, sedan based or open vehicles 10.99 (1/4 mile)/7.00 (1/8 mile) and quicker.
Full roll cage mounted at a minimum of six points (Figure 2). Sedan type vehicles that are constructed in such a way that the body could separate from the chassis/roll cage in an accident, mesh or net of a maximum 75mm (3 inch) is required to be fitted to the roll cage over the driver's head to retain the driver's limbs within the cage area in the event of a roll over.