Hiiii! Oren!
Well you said yourself Oren, the shinigami wouldn't attempt to destroy a building because they cant get life from it. Why cant they get life from it? I'll tell you why, it's because they don't believe the building is alive. The deathnote as such doesn't care about hte buliding. If you believed the buliding was alive and I mean really believe not just wished hard enough that it was, then you'd most certainly be able to glean life from simply from the fact that you believe there is life left to be taken from it.
The deathnote isn't limited by the boundaries of what is alive, it's the users who are... in fact if you were to continue to stand to the fact that the deathnote could only kill humans then by reasonable deduction it implies that the deathnote knows the difference between a human and non-human life. Not just that, it also has the means to kill such a life if it exists. Couldn't one then argue that the deathnote was actualy "alive" and so one could presumably use one deathnote against another!
