Please help me to refresh my memory:
The way you want to do this in a simple wind load analysis is:
1. Determine steel roof deck type gage.
2. Compute G' value from manufacturer's catalogue information.
3. Determine an equivalent thickness of flat steel plate that will have G =
4. Use this thickness as the property of your "plain stress" element which
you will put in your model.
If I'm forgetting stuff, let me know. Sorry, it's been awhile since I've
done this and I have to be sure I've got it right.