Do you disagree with the idea that with knowledge and time humans have the potential create any material thing?
If that's a reasonable thing to assume. Then we could simply just build a human from scratch.
Then, add on the entirely subjective experience each of us has of consciousness: it's not obvious that subjectivity is created or come from machines. Each of us has one good example, and the rest is intuition, induction. At best, "You can build machines like us, because we ourselves are the proof," is a wishful project, rather than a proof.
Machines are just physical systems that perform some work. This includes cells, biological systems etc
If we built a human from scratch at atom level detail then it would be reasonable assume it would experience the world as we would. By definition you would have created consciousness.
I'm not sure whether this clone would or not, but we don't have a good basis for either. If we built one, we should act like it does experience things, but that's on moral, not scientific grounds.
That human beings are machines is something that needs to be proven, it can't simply be taken for granted.