Regarding cages. ASN Canada says
Although FIA Article 253.8.3.3 specifies the safety cage material as CDS (Cold Drawn Seamless),
DOM (Drawn Over Mandrel) tubing may be used as an alternate material in respect to the
following: Main roll bar, front roll bar, lateral roll bars, lateral half roll bars, their connections
(drawings 253-1-3) and one continuous door bar per side will be at least 1.75"x.095". All other
parts of the safety cage will be at least 1.5" x 0.095".
The Autopower cages meet this standard. They are .120 wall DOM tubing. The rest of it depends on what the design needs to be.