There are a few ways to make the baggy/wrinkle effect. Hope this helps 
Sculpting is one method that if you understand how to properly make a part that can easily be sculpted under 10k tris and are able to do that without leaving dents/weird mutated planes then it can be effective. From the photos given, it does look like they are sculpted but it may just be the smooth settings.
Another way is to make a block clothing around a rig then using angled loop cuts expand, shrink and drag the layers around to give the impression of being baggy. (A guy on Youtube called Furapan made an ok video about it)