I went sixteen floors once, but it seemed was too high. I backed off to eight, and eventually removed the building altogether - made eight or nine one to three story buildings out of it instead.
Since you can just insert floors one after the other, I imagine you could go ridiculously high before anything would break from the weight - maybe 40 storiesjust keep adding - probably at some point the first thing that would cause problems would be that you would have too many lights in, say, a forty story building, for the gauge of wire at the bottom, overheating it and/or getting noticeably dim as you reach the top.