I asume you are refering to challenge events, as the minimum level of protection for these events is a correctly fitted manufacturers hard top, although a roll cages or bar is recommended. it may how ever be in the event SR's that a cages is needed for class 1 and 2. the SR's will be event specific, have a look at the post below and have a look in section K of the current MSA blue book, the norm is front and rear hoop made from one pieace of bar. with front and rear hoop and rear stays going down to the chassi and welded or bolted to spreader plates. The best option is to contact the events you are wanting to enter directly to confrim.
have you got a photo of you vehilce I will have a look and see what we would say for our events if it helps Grim