I have tried Fredo's scale tool, but it too uses the "bounding box" to specify base points for scaling. If you open up the file I've attached, you'll notice that I've dimensioned the vertical "bulge" of the arc. Note that the corner of the surface is not at the lowest vertical elevation.
So when I go to scale the entire object, pulling the bottom blue only grip does not refer to the "corner", it is referring to the lowest vertical elevation. Essentially, the 2nd bounding box image that I posted earlier is where I would LIKE for the bottom edge of the bounding box to be, except that I want to scale the WHOLE group unidirectionally using this smaller bounding box. In other words, the vertical "bulge" height becomes the reference height by which I want to scale.
For example, I would like to vertically scale the object referring to the 24' vertical height to a new height of 27'6". I understand that if I get out the calculator and divide the desired height by the current height, and then manually enter the scale ratio down to the nearest thousandth or even ten-thousandth, I'd get a somewhat accurate dimension.
This can get cumbersome and time consuming pretty quickly though in a larger model, particularly when I want the object to be scaled from a specific point (being limited to bounding box scaling means that I would potentially need to reposition each object which would be scaled using different scale factors).
Please let me know if I've made this any clearer or more confusing.
Roof_segment.skp