Buying the proper ones may save some headache and extra expense later. I dropped on a set of MG-R Mk.2 hoops for just over 100 quid, so if you are prepared to wait and bide your time, bargains do come along. Just remember when fitting hoops, some of the sloping forward type, such as the MG-Rover Mk.1's will interfere with a glass rear window on the soft top, if you have one on your car.
The MG-R Mk.1 and 2 are both designed to take some of the impact on actual roll over, unlike the cosmetic ones you can get.
Sundance