I am wanting Sentient mechanical beings similar to the Transformers, robots in the movie Robots and LEGO's Bionicle. I want it to be an all robot world.
Ok, so it's not that you want an exploration of the implications of self-aware technological aftifacts.
Instead robots are more of a stylistic choice.
OK, I think in that case it depends on how much choice or 'cool stuff' you want to give your players.
If you want to have the robots be upgradeable you need to decide how that is done. Class progression? Spend feats? Spend cash? As a replacment for magic loot?
Are there different chassis? Are there different basic sets of gear/add-ons?
For example one way to do it might be to have a half a dozen different basic chassis designed, roughly analogous to a race in D&D. Each one provides a movement rate, basic stats (or stat modifiers), AC and a few special abilities.
Then your class gives you a skill list, set of abilities and a basic build-up that provides your starting equipment/accessories.
So you might have a scout chassis with high speed, small size and high dex but low HP. There is also a goliath chassis of large size, high hp and strength but poor speed and manuverability.
Then you might have a guardsman class which provides basic skills, a built-in melee weapon, and armour plating. A hunter class gets skills, improved sensors, and a ranged weapon. A hacker class gets advanced programming skills and an antenna system that allows it to over-ride other robots actions in basic ways at low level and better ways at high levels.
Finally you have a set of feats like 'melee weapon upgrade', improved armour, or jet pack.
For added complexity you might have a defined set of upgrade slots in each chassis type and each feat or class ability uses up a slot, and must be either upgraded or replaced. While increasing build complexity this might simplify play by reducing someones ability to combine things in weird ways, or to spread themselves too thin.
