I can see 2 things I'd change about that roll cage.
First, make that left side bar actually structural, that bent footbox bar is worthless as a load bearing member.

Second, tie the horizontal member on the rear bars with the members directly underneath. They're a few inches away, why not make it that much better?

Also, the gussets where the cage meets the body could be a little beefier and larger area. In the event of a rollover, you want to spread force over a larger area, not a smaller one.