So one of my players has fallen in love with PR and of course Him and me were huge fans of Zoids.

How would one do the mecha style RPG system?

I mean like Weapons damage when zoids/mechs have guns that measure like 108 mm or 200 mm guns for small/medium weapons? (Liger Zero's chest mounted shock cannons where 108 mm and considered small)

I just need building blocks for this set up as we are gonna run this on a homebrew idea for a system but I need help with the set up.

Any help is welcome. The system will have guns, armor, defense, CAS if needed, Weapon and Armor Upgrades, and have to take into account favored battle styles (For Zoids it would be Air, Ground, and Water.. if you favor water and your fighting in the air he would gain no bonuses maybe penalties to it but in water he gains a lot more bonuses.)