By ruffles, do you mean something like pleats? If so, you can only do horizontal type pleats AFAIK.

Also, by layer, if you mean something like a long sleeve shirt under a t-shirt, IE layers of clothing, than you might be able to do it by making each item separately then adding them in Poser, however, I have a feeling that this might give the cloth room fits, since you will most likely have too many clothing collisions.