I'm considering a game concept where you build robots for war, but with limited parts.  An RTS Style, but instead of learning to build the wheel, you have to find 4 wheels to make 1 vehicle.  Are there any existing games like this?  

I don't think you are describing a RTS game, except in the most formal sense of featuring multiple units that can be given orders in real time.

Steady resource influx and resource attrition is a cornerstone of typical RTS games: there can be an occasional blunder or stroke of luck, but on the whole victory goes to the player who makes the most efficient use of resources (by turning them into units and using units to destroy, over their lifetime, units worth more enemy resources than their cost).

If instead, you have peon units exploring the map to collect parts of dangerous units, and in a later phase assembled dangerous units doing real fighting, very different patterns are to be expected:

• It can be a game about exploring and scavenging, in which the first player who completes a killbot wins by using it to exterminate the enemy without significant opposition (and without significant fighting, only a boring final demolition)
• It can be a game about building the killbot as fast as possible, for all practical purposes a planning and dexterity puzzle in which the map doesn't matter except for constraining building placement.
• It can be a game in which killbots are easily built, the fastest builder has a modest advantage, and the main activity is a fair battle (in fact, a very non-RTS-like arranged duel at a leisurely place, since with nothing left to build or collect there is no time pressure) between very similar small forces.