Spear_Master
Shouldn't he have asked for Moat Cailin if he wanted a castle? It would serve to fortify North and as his residence. Or maybe some point at ocean shore so he can make another port for trade? It really makes no sense at all to have another castle near to Winterfell, I mean he's Stark anyways, he can just stay there. Castles take a ton of work and resources.
look at the maps where white knife and long Lake. It's strategic location. you can travel towards winterfell and Bolton lands via water. these rivers go straight to sea from manderly lands (white harbour). Yes Moat Cailin is a extremely valuable strategic location . but you want to build an industrial area there? it's not good place.