[Trod Upon]

Just as the existence of a car is proof beyond a reasonable doubt of a designer of that car, so your body is proof beyond a reasonable doubt that Someone designed you.

Apples to skyscrapers comparison. Nobody is arguing that cars are anything other than a created work. A product. But that is not the case with man, or the apple for that matter. By your process, if one believes that there is proof of God's existence, then God himself must surely have been designed by someone. If not, you're left with the same old problem of the uncreated creation. If something as complex as our conception of God can exist without cause, why not the universe? Positing God doesn't really solve the problem; it just allows Him to become the placeholder for all the uncertainties formerly attached to the universe.

[PapaNew]

By your process, if one believes that there is proof of God's existence, then God himself must surely have been designed by someone

Not at all. The only thing you know is that living things whose parts are intricate and work individually and together as a unit with a purpose are evidence of a Designer who is intangible and otherwise unknown to you. You go outside the scope of the discussion when you try to prove the non-existence of an intangible Designer by things you don't understand about the intangible Designer. That is entirely another discussion. By definition, the Designer is not necessarily limited by the limitations of the design (you and I).

[Celtic Cross]

"By your process, if one believes that there is proof of God's existence, then God himself must surely have been designed by someone."

Nope. You cannot apply the physical limitations of a creation to a spiritual, metaphysical being.

An analogy; as a programmer, I can make a game with limitations of my choosing. I can program sprites that will be subject to an animation-loop for a set period of time. None of these limitations apply to me. The very concept of an animation-loop does not apply to me.