Screen porch foundation and walls??

[Elovia]

Welcome to the forum Nail Bender.

I'd suggest you start with a deck, make the deck railing invisible. Then, open the deck's room specification dialog and set the framing properties on the Deck tab; also on the Structure tab, put a check mark in the box for "roof over this room". Then, and use the Build Advanced Deck Framing tool to get the post and beam foundation. Either before or after you do that, take a look at the following link which should provide insight to creating the screens.
http://www.homedesignersoftware.com/...?faqNumber=748

Good luck.