Cool Breeze,
If its not bolted or indeed welded to the chassis it is not a valid roll cage more another bling accesory. If you want it to be a valid cage check out the MSA website. It lists the specs it has to conform to:
Certain material specs,
Shape and design,
Minimum height width,
You can obviously change the design and make an all new type but it will need to be submitted for approval in which destruction testing may be carried out and many manufacturers avoid this duer to the high cost of build for tried and tested well know designs.
Check ouy Whitbread-offoad.com £400 you can get a weld in kit for a truck cab that welds to the chassis and conforms to all current msa specs IF you use the correct spreader plates (6mm I think for ARC events).