Even if I pay a guy to put my block at the top, I don't own the pyramid unless I bought or was given ownership of the whole thing.
If I have a lot of blocks out on my property, and I let people make a pyramid out of them under no contract (like for fun), the pyramid is mine: I still own all those blocks, and I have the right to say that people should not destroy the pyramid after that, since it's all my property anyway.
If they all but build the pyramid and I have to pay a guy to put the last one on, it's still completely mine. This is like when companies pay a guy to put together existing software and hardware to solve their specific problems. What you are paying for is the labor. Companies do a lot of this. As long as I own or they can rightfully sell me the pieces used in addition to the labor, you can see it's completely kosher. The same applies if the pieces were released into the public domain for everyone to use freely - in that case I own them as much as anybody else.
If I draw up contracts with workers to build a pyramid, then I'm obligated to honor all those contracts. If the pyramid is built and I didn't pay them, then I stole labor from them. It isn't that the pyramid is theirs, it's that the labor they already gave me (and can't take back) was stolen, and I owe them the money I agreed to pay.
What seems to be more common is something like this: I contract with some guy who says "pay me $2 million, and I'll get you a pyramid built." Then he draws up contracts with lots of workers, who build the pyramid. But when I pay him, he doesn't pay the workers like he told them. In this case I own the pyramid, since he persuaded the workers to give him labor, which he then gave to me. But that $2 million isn't all his, since he owes the workers what he agreed to pay them.
Unfortunately, that kind of stuff also helps to build fortunes. But I hope I convinced you that it is either a clear-cut case of theft, or not really a problem.