If space is a consideration in your remodeling project, you might want to consider building a winding staircase. You can build this simple version yourself. Think of it as a stack of wooden boxes with a portion removed for each successive step. Build each box step in advance and stack them on top of each other. Secure each level with panel adhesive and nails, then finish off with a straight run to reach the next floor. Remember to check with your local building inspector.
For more on stairs, consider:
How To: Paint a Staircase
Building Winding Stairs (VIDEO)
A “Step by Step” Solution: Pre-Cut Treads and Risers