I don't think that's something that would be solved with exercise, you're probably walking retarded and landing weird with one of your feet for whatever reason, which is actually not that hard a habit to develop. You could have flat feet or be wearing the wrong shoes too, which could exacerbate the retarded walking issue.
Think: There are loads of people out there who are flabby and aren't constantly twisting their ankle. If not having muscular enough legs caused you to roll your ankles, leg/ankle sprains would be the #1 cause of injury in the western world considering how fucking fat everyone is (although fatness does tend to cause people to walk weird and increases the risk of leg/ankle injuries).
This is almost definitely a technique problem, not a strength problem.
Spend some time to focus on walking properly, pointing your toes forward, landing with your heel and rolling, and make sure you're wearing proper shoes. I'm assuming you aren't obese. If you are fix that too.