The design was inspired by Stonehenge and the Pantheon.
http://www.cathedralparish.org/architecture.htm#Intro
My thought is that they planned a second story, but ran out of money before they could add the roof and curtain walls. It has to be one of the ugliest church buildings that I have seen.
I visited a town south of Indianapolis one time (Columbus?) which was proud of the architecture of its churches. A few of those were quite ugly as well but nothing in this league.
Here's a selection:
http://www.bluffton.edu/~sullivanm/colselsaar/elsaar.html
http://www.bluffton.edu/~sullivanm/birkerts/birkerts.html
http://www.bluffton.edu/~sullivanm/colsnxian/colsnxian.html
http://en.wikipedia.org/wiki/First_Baptist_Church,_Columbus,_Indiana
Well, I'm glad to see that it's not just us Catholics who've allowed the uglification of our building stock! There are so many ugly, unglorious and unedifying Catholic Churches around that it's hard to keep track...however 'Fort Bennison' takes the cake. That's simply the ugliest bldg I've seen...church or otherwise.