The first thing I offer to someone wanting bigger legs is to ask them, Do you REALLY want bigger legs, or would it just be nice if you had them?
Legs are a muscle group of high tolerance. It takes a balance of both intensity and volume to get them to grow for most, and while many choose to view themselves as hardgainers, it most usually is the fact that they aren't willing to embrace the discomfort that comes from training their legs to grow, IMO.
Here is a favorite quad routine that worked for me...
Warmup by supersetting extensions and curls, ATERNATING each leg per rep.
*Barbell lunges-
Start w/ a light weight...even just a bar for 10 reps
Increase the weight each set, until the 10 reps aren't met, no matter how many sets it takes.
*Front Squats-
Choose a weight heavier than the last lunge set...aim for 6-8 reps.
Again, Increase the weight per set until the weight at 6 reps is a struggle.
*Regular Squats-
Choose a weight heavier than the last set of front squats... aim for 3-5 reps
This routine may seem to be too much, but consider the following...
Each excercise offers pre-exhaustion for the next ='ing great intensity.
The natural progreesion of weight from excercise to excercise = no wasted sets, as each set serves as it's own working set PLUS the warmup for the next!
By the workload always increasing, once blood is forced into the muscle, it is captured there, due to the synergistic effect of the progression. That's what translates to volume.
Keep in mind, this routine is not based upon a dogmatic rep range. It can be done for high reps or low reps! Whatever your preference. And as far as sets, in my own workouts, I've found that usually 4 sets of lunges, 2-3 sets of Front Squats and 2-3 sets of Regular Squats are sufficient, as long as the selected increased weight stays w/i the rep range.
If anyone's interested in knowing more, let me know. Hope this helps!