Stairs from Garage to Basement

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Hi Guys,

I've been trying to figure out how to properly make some stairs leading from the garage to the basement.

My first problem is that I want the "hole" in the garage floor to be flush with the garage floor - that is to say the top of hole is flush with the garage floor and the bottom of the hole is flush with the basement. I do not want any kind of half-wall around the stair well. I will do a railing around the hole.

Any suggestions? Whenever I use the foundation tools to make the hole, I get the stem wall at the same height as the rest of the garage, and when I try to lower the height of that wall, it affects the entire garage, not just that wall.

I've attached an image of what I'm trying to do.

Any help would be greatly appreciated.

Thanks!