Making a New custom livery

I am trying to create additional liveries (SKINS) of the MB339APAN. I know very little about creating a livery, and it seems to me that the megapack will be useless to me as it appears that it is oriented around the A320.
There seems to be very little info on the NET about creating a livery for anything but the A320.

Is there anyone out there that can tell me what files are needed to complete a new livery?

Thank You