You need a modeling program to create clothing, unless you want to attempt piecing it together with primitives and the grouping tool, which is possible but won't produce very good results. A simple skirt could be built with primitives and either rigged or clothified. The fitting room will group a clothing object for you.

You can download a free modeling program like Wings3D or Blender. I haven't used wings in ages so I'm not sure how much it's changed but with blender you could practically draw the shape of the clothing you want around your figure and create the model that way. Even if you've never touched a modeling program you could build a simple pair of pants for any figure just using 3 or 4 basic modeling functions and it would fit the figure the way you want it.