http://en.wikipedia.org/wiki/List_of_American_football_stadiums_by_capacity
Above is a link to a site that gives stadium size (number of seats) in descending order. Most of the top college teams play in large stadiums and to large crowds (80,000 plus). For example: Penn St. (107,000+), Michigan (106,000+), Ohio St(102,000+), Tenn (102,000+), Georga (93,000+), LSU (92,000), Alabama (92,000+), UCLA 91,000+), Florida (89,000+), Auburn (87,000), Texas (85,000), Nebraska (85,000+), Oklahoma (82,000), Clemson (80,000).
If BYU wants to considered among the top 20 teams in the nation then we should have a stadium at least equal to their average stadium capacity (around 85,000)