Mick is right, the square cube law has to be taken into account -- but that doesn't mean building scale models is impossible or would teach us nothing. Take a look at this video at 3.06 for an idea of what was built to understand structural disasters before computer models were available to structural engineers.For what it's worth, I've head the scale model idea won't work because you can't scale gravity. Makes perfect sense to me, but I'm not a SE.
In the case of the Towers, a model like this has never been made, even in simplified form, although we are told the "gravity-driven collapse" of those structures was in principle quite simple. Needless to say there are several examples of physical "gravity-driven collapse" models that spectacularly fail to experimentally demonstrate what we are told was what happened on that day, and there are none that support the official collapse theory.