I think I have the answer. In order to add a wall type to your library browser, follow these steps:
1. Open new plan file.
2. Select Wall Type Exterior
3. Draw a segment of wall in the plan
4. Open the wall and select copy. Then rename the copy you just created.
5. Edit the wall assembly and click OK to exit the wall assembly when done.
6. From plan view, click on the wall you just created and add it to the library with the button at the bottom of the screen.
It is very important that you COPY and RENAME the wall type. If you simply edit the default wall type that comes with Chief and save that to the library without copying and renaming it first, this is where the material conflict happens. It is the same for REVIT, you must duplicate and rename in order for it to work.
Once this is done, from the library browser you can just click the wall type that you created and draw it. I have mine all set up like this. I also created a full template for residential with all the standards I typically use, including dimensions. So I use both in tandem to speed up my process. Overall, I think it took me about 8 hours of fiddling with everything to get to where I am happy with my custom defaults.
Hope this helps.