If he's mainly a coverage LB you could see 75 end build and not be terribly lacking, but if you'd like your dot to be more multi-purpose than 80 would be a good end build.
Here's one of mine for reference, he's got a 19% missed tackle rate (about 1.06 per game), mainly built as a coverage guy. (100 tackles attempted, 19 missed)
http://goallineblitz.com/game/player.pl?player_id=1976397&playoffs=0Any more tackling you could get on top of that would make your dot more effective, especially with the Textbook Tackler VA stacking on top of it.