I know some other posters have listed the stats, but I figured I'd look up as many stats as I could to try to make me feel better about this hire and compile them all together. These numbers are going to be from his time as a DC only.
2012- Penn State
23rd Rush - 128 yards/game
50th Pass - 255 yards/game
29th Total - 353 yards/game
16th Scoring - 19 pts/game
2011- Auburn (was only at UCF 33 days)
94th Rush- 189 yards/game
51st Pass - 218 yards/game
81st Total - 408 yards/game
79 Scoring - 29 pts/game
2010 - Auburn
9th Rush - 109 yards/game
108th Pass - 259 yards/game
60th Total - 369 yards/game
53rd Scoring - 24 pts/game
2009 - Auburn
78th Rush - 156 yards/game
57th Pass - 218 yards/game
68th Total - 374 yards/game
79th Scoring - 28 pts/game
2008 - Minn
68 Rush - 143 yards/game
93rd Pass - 240 yards/game
80th total - 383 yards/game
61st Scoring - 25 pts/game
It should be worth noting that Minn had the worst defense in FBS in 2007. They won 1 game in 2007 and went 7-5 in 2008. So while those numbers aren't exactly stellar they are a huge improvement from the year prior.
2003- Duke
63rd Rush - 158 yards/game
53rd Pass - 217 yards/game
57th total - 375 yards/game
76th Scoring - 29 pts/game
2002 - Duke
28th Rush - 120 yards/game
102nd Pass - 254 yards/game
65th total - 375 yards/game
83rd Scoring - 29 pts/game
2001 - GT
23rd Rush - 117 yards/game
53rd Pass - 216 yards/game
32nd Total - 333 yards/game
37 Scoring - 22 pts/game
2000 - GT
12th Rush - 94 yards/game
114th Pass- 285 yards/game
70th Total - 379 yards/game
21st Scoring - 19 pts/game
1999- GT
89th Rush - 189 yards/game
100 total - 413 - yards/game
93rd Scoring - 30.3 pts/game
What I take from this is that Roof is aggressive on D to stop the run but doesn't seem to be too great at stopping the pass. While I think this is the approach Tech needs to adopt to win games, aggressive D that can pressure the QB and stop the run, I'm not sure I like Roof as the coach.