Revit :: How To Model A Parametric Unit

I'm trying to model a parametric simple unit in Revit. So, I decided t use the generic family template. I want to model a rectangular unit with exterior wooden wall and interior steel frame. I have three problems

1- I have imported structural column profile into the family, but my problem is that I cannot align the section to two reference line. For example, I want to align the top of the column to the top exterior wall, and align the left side of the column to the left exterior wall; but I can just assign of these sides.

2- I've imported structural framing family in my generic model, but I cannot assign a parameter to the length of the beam, and the length is constant, and I can change the length just in 3D view. Do you know how to assign a parameter to the length?

3-I couldn't use the predefined walls it the family, so, I used extrusion. But I couldn't use the Revit windows family on the extrusion walls. Is there any way to use the predefined wall systems in Revit to be able to use the windows families?

Here is the picture of my model: