Not to put a downer on your idea but I looked at doing this as well as building my own cage. I wanted to use cds to build it all. It's not cheap to begin with but then a ordinary pump action tube bender isn't really going to do the job and ideally a mandrel bender is required, then there is measuring and if you mess it up then it's start again, then the ally sheet, the time factor etc. I added up and was looking at 180 quid to do it my self and that was materials only, that is if I didn't mess up, but then there is the north off road kit which I think is £350 can build it in a day, will be perfect, all ready pre notched.