A teeny weeny bit more info please as your first question is to open, do you mean build up for electrical reasons or do you mean how is mass lamination performed....
What does L/S mean, care to elaborate, what are we referring to litres per second! again more info...
A stackup drawing defines finished thickness and each layer of conductor and dielectric.
Vendor can choose either doubled sided copper in a multilayer and how many layers of pre-preg to make up layer thickness, for example in a 4 layer board.