Here's some examples of mine. some have round cakes as the top tier, some are 'turned' (not perfectly aligned 'square'), but they will give you some ideas:
http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=538243
http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=412533
http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=303533
This is a five-tier, but if you take your hand and cover the bottom two, you'll get a visual:
http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=199773
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