Kant and Metaphysics

Kant makes an enormous amount of claims regarding mathematics and how the laws of geometry are not bases upon the objective themselves but how we perceive the objects. Which is true, we base these rules of geometry upon how we perceive the outside world, but that really all we have to go by. With this argument Kant claims that our geometric laws or rules have "no objective validity because we cannot see how things must of necessity agree with an image of them." But how much does it matter that we build the laws of mathematics from our perception of objects? If we have this law of Pythagoras which says that the square root of two sides of a right triangle is equal to the square root of the third side. Is this theorem not valid even when we ourselves create a right triangle using 2 by 4s. When we go beyond merely perceiving an object or shape and create it ourselves. Are we still merely perceiving an object of our own creation or does this idea of perception change. Does our priori foundation develop into one of posteriori? If all knowledge is based on perception of objects and we are unable to trust whether our perception is an accurate representation of the object in itself, then the laws of mathematics are merely laws that attempt to explain the world we perceive and may have to validity at all.