Could moving land mass alter Earths gravity?
No, these building are still tiny compared to earth's crust mass distribution. One would need to build whole mountain ranges to detect changes in earth gravity field with high precision instruments. And even those wouldn't changed earth orbit measurably because even a mountain range is tiny compared to the mass of the whole earth.
However mountain ranges (and their rock density) do have a measurable influence on earth's gravity and this measured by satellite missions like grace.
PS: And no, it's not a stupid question. But you could submit it to xkcd's "what if?" section ;) .