i haven't been to the ou campus in 15 or more years, but i don't recall it being ugly at all. baylor has a pretty campus too.
you want UGLY, among campuses in the b12, i would say the fuskers are among the worst. that stadium looks like it was designed by a stalin-era eastern bloc factory worker. i have also heard that t-tech's campus isn't that great but i don't speak from experience on that one.
osu used to be nothing to look at either, but with t-boone, i suspect it is improving a lot.
kjuco state ain't much either.
in terms of pretty campuses, CU is obviously #1 and not just because of the flatirons. the red tile and stone throughout lend an architectural consistency that you don't find other places. and, in terms of stadiums, ours' ain't the biggest, but it is very well-designed and nice to look at.
i would put austin second and lawrence third. i would put stinkoln as the 12th out of 12, reserving a potential swap for 11th with t-tech as i have not visited there.
i had fun at texas a&m too, back in the day, but i don't recall the campus being much to look at. mizzery isn't very nice either.