Ok, so for a good map we're gonna wanna think about where we want things geographically as well as climatically. If we're in a cold wasteland we'll be far north. My suggestion, we should build out from where we want to start, that way we at least have somewhere that we can bring us all together and we'll adventure out from there.
I'm partial to starting out in a colder climated environment. Either a temperate area during the winter or a place to the north.
BTW, Ambra, I turned Legends into a D&D campaign and one of my friends is actually remaking the map... because I didn't realize it at the time but you literally just took Westeros and tossed it at me as a map XD (I hadn't watched GoT at the time so I didn't know).