A fetus becomes a human when it has the capacity of living independent of its mother's life support system. Until then, it is not really a human BEING, it is the prelude to a human being.
This is not true, a fetus is a living human life form, with its own DNA, nervous system, brain function and heartbeat. It will develop into an infant human being, at which time it will still be dependent on the mother, or someone, to nourish it, support its life, and allow it to reach its next stage of development. It can be no other form of living being, other than human, we've established this through simple biology already.
You can keep arguing that a growing and living human fetus is something other than human life, all you like... you've given me NO supporting evidence for this opinion, and without any supporting evidence, your argument fails. Sorry.
Here... let me make it easier for you... Once conception has occurred, other than time, what other elements or ingredients are needed to make it a human life? You keep saying it's not human life or a human being, but you need to indicate, what is needed or required after conception to transform it into human life. How can it change what it is, if there is no change in properties?
As for your house building analogy, it really doesn't apply to what we're discussing with regard to physical biology of living things, but I thought of this and wanted to throw it in the mix... IF I came along and filled your hole full of water, making it impossible for you to build your house, would you consider that I had destroyed your future home, or merely built you a swimming pool? Would you sue me or thank me? I think we know the answer!