those exhaust cages are common for roof of africa. Always a bit of an argument about the additional weight they add (about 4kg) but do work, but often there is a tradeoff - short story is that a 2t pipe is always going to get in the way
but yes, you will need to make it yourself (I believe it is better to make it with mild steel rather than stainless). Force makes a similar one out of aluminium, not sure if they do it for gas gas