TheFork users who ate in Munich have said really good things about Medici, Natraj and Nam Giao 31. Maybe you should give them a try!
Some of the more popular Winter terrace restaurants having a terrace in Munich according to TheFork users include:
Conti Restaurant, with a 9.3 rating
Le Voyage, with a 9.3 rating
Tepsija, with a 9.3 rating