How does Wall of Roots interact with +1/+1 counters?
They ignore each other completely, so the Wall of Roots will have both a -0/-1 counter and a +1/+1 counter (which has the net effect of having +1/+0).

The only reason +1/+1 and -1/-1 counters interact with each other is because of this state-based action:


  704.5q If a permanent has both a +1/+1 counter and a -1/-1 counter on it, N +1/+1 and N -1/-1 counters are removed from it, where N is the smaller of the number of +1/+1 and -1/-1 counters on it.


There is no similar rule for -0/-1 counters.