cage first. i dont know how much i would listen to these mid-west east coast dudes about building a desert truck.. or mark.
my opinion, aside from saving up and doing it all at once, is to do the cage first. since the cage is what's gonna keep you alive, for one. Secondly, the cage is such an important part to the rest of the components (ie: shock mounts, seats, glass, etc..) it might be handy to have that in place before everything else. But still, all at once is best, cage first is 2nd.