If all you need is a flat, that's a better option than purchasing them, in my opinion.
Even a low relief building is pretty easy to make, especially if you download some textures from the web. Or you can use commercial texture paper and door and window castings, which is still cheaper than buying a model kit.
Connecticut Valley Railroad -- A Branch of the New York, New Haven, And Hartford
"We don't stop playing because we grow old. We grow old because we stop playing." --George Bernard Shaw