Revit families: How to parameterize an inclined reference plane to move horizontally by a dimension?

[MCalza]

I have the family .rfa that I attach and it can be seen in the next picture (picture 0):

I want to modify the dimension A, and that the inclined plane extrusion moves with it (see picture 2). I don't want is that it do and you can see at the next picture 1:

 That's I want to do (picture 2):

 

Do you know how to do it?

Any advice or suggestions?

Thank you

[barthbradley · Accepted solution]

Use a Reference LINE in Elevation View and host the element to the top of this Ref. Line/Workplane in Plan View. 

Here. Something along these lines...

[barthbradley]

Revised one: 

[syman2000]

Reference Line is the way to go like @barthbradley said. Make sure you have a reference plane where you define the start of the angle. Alternatively you can also use nested family to flex it so you don't need reference line. See attached

[barthbradley]

I would definitely agree (and urge) that the element being driven by the angled Ref. Line be a nested family (Work Planed Based) and hosted to the Parent Family Ref. Line.