I think I'm going to do the panels for the building ahead of time, but I need to figure out how to do the stairs. I saw this great photo online. It's JUST the stair case, so I wouldn't need it that big. Mine will be attached to the building.
What would you use?

Hmm, picture didn't post...trying again.

Okay, I cannot figure out how to get the photo attached, but it's very similar to this;
http://cakecentral.com/gallery/1875911 by CakeAnnie.
So, what would I use for the stairs?

Depending on how large your building is, could you use rice krispie treats covered in fondant or if the building details are pretty small, just gumpaste/fondant? Either way, you could make them ahead of time, too.