So that I can have some spaces to wear Down or Fleece inside the jacket?
Normally Large size shell is too large for me, or I should buy the same size so as fit as possible?
I think the answer is as simple as:
There are several different layering systems find what works for you and try everything on in store. If you would like to purchase something online and cannot find the same model to try on in store, at the very least try on some gear from that same manufacturer to get an idea of their fit.
Try contacting a manufacturers retail store close to your location and inquire about their return policy. For example I know in Canada I am able to buy North Face from their website, have it delivered to my home address and if it does not fit I can return it to the retail location in my city no questions asked.