One of my favorite builders when it comes to textures is Anduraga. He's given some great tips for the Waterdeep project and other projects over at the Weave. He recently posted a great list of tips for people looking to build good exterior areas. Here's his intro:
I find that many people find area building a very difficult task, and when they do make areas, they are often basic, because of the lack of tutorials, tips, etc. I can relate that to somewhat in a different department. Scripting isn’t really my strong suit, but I can manage to do the basics. But anyway, to the point of this post/thread. I have designed this thread to help new builders, adept builders and even master builders with tips and tricks of the trade. I haven’t checked out many of the tutorials on the vault (Shame on me, I know), so all this stuff I’m throwing out here now might already have been covered.
Check out his list of tips here:
http://nwn2forums.bioware.com/forums/viewtopic.html?topic=578694&forum=113