I've had a few questions about some of my screen porch videos because I skipped over some of the basics.  Here's a video that shows how to create a screen porch room...define the wall type and the railing wall type.  I use "panels"...so, you will have to create a railing panel.  I have also created a video on how to make a panel...it's on my YouTube Page.  Let me know if I've missed something...or, if a guru has a tip or better method feel free to comment.