Try using the Surface Label Tool.
You can choose which face of a wall, roof, slab to reference.
And/or you could create a schedule of the exterior finished surfaces.
If you post a pic of what you want it to look like, we here can be more specific with our answers.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"