Stairs with 2 simple stringers

[makis]

Hello,

I want to design a simple staircase with only 2 straight stringers. The concept is:

-Metal channel stringer on either side of the treads. No cuts on the stringer. The treads will attach to the inside of the stringers with brackets.
-Open risers.

How do I do this in Home Designer Pro 7.8b?

The closest I've got so far is 3 notched stringers. Not right for the project!

Thanks