Reflection Array

I am trying to call a method in a 3rd party dll via reflection. Their method looks something like this:

void SomeFunction(ref A[] b)

I can handle the ref portion but I dont know what to do concerning the A array. I was thinking maybe I could use List<A> and then call toArray. The problem is A is defined in the 3rd party dll too and has to be gotten via reflection. I dont know how to create it. Any ideas?

Thanks in advance.