I actually did this about 5 years ago in a lot of detail. 7 tiers. Here are the first 3 tiers.

If I was doing it again, I'd probably make a few changes (such as moving Virginia up 2 tiers to bottom of Tier 2, moving Wichita and San Diego State up to 3rd tier and dropping Temple and UNLV down to 4th tier).

Top tier:
North Carolina
Indiana
Kansas
Kentucky
Duke

Top tier, but not a notch below:
Michigan State
Connecticut
Louisville
Michigan State
Syracuse

2nd tier:
Georgetown
Ohio State
Oklahoma State
Villanova
(middle of 2nd tier)
Arizona
Cincinnati
Illinois
(bottom of 2nd tier)
Arkansas
Marquette
Maryland
NC State
Florida

3rd tier
(top of 3rd tier)
Georgia Tech
Kansas State
Louisiana State
West Virginia
(middle of 3rd tier)
Michigan
Nevada - Las Vegas
Oklahoma
Purdue
Texas
Utah
Wisconsin
(bottom of 3rd tier)
Arizona State
Boston College
Brigham Young
Butler
California
Creighton
Gonzaga
Hartford
Iowa State
Memphis
Missouri
Notre Dame
Pittsburgh
St. John's
Stanford
Temple
Tennessee
Vanderbilt
Wake Forest
Xavier

The next tier had 41 teams in it.