High rep routines are helpful and should be done at least once a month to keep capillaries open to increase blood volume, but to really put on leg size try multiple low rep sets, changing set and reps each workout and switching exercises every 4 weeks. This routine really worked for when trying to build leg size:
Week 1 & 5
Squats or Front Squats 6x4
Good Mornings or Deadlifts 3x6
Leg Press or Hack Squats 2x8
Week 2 & 6
Squats or Front Squatsx6,4,6,4,6 (wave method)
Good Mornings or Deadlifts 4x10
Leg Press or Hack Squats 2x6
Week 3 & 7
Squats 8x3 or Front Squats (60 sec rest periods.)
Good Mornings or Deadlifts 5x8
Leg Press or Hack Squats 2x5
Week 4 & 8
Squats 2x20
Good Mornings or Deadlifts 2x20
Leg Press or Hack Squats 2x20