You may want to start with the Bar Aspect Ratio measure. It takes in a floor plan aspect ratio and an area. You can alter the aspect ratio (length vs. width) and as a resort the perimeter to floor area ratio. It would be pretty easy to modify a copy of this to take a perimeter to floor area as an input as an argument, then internally convert it to an aspect ratio that meets that target.

The downside of the current approach is that as the perimeter to floor area ratio gets bigger you are increasing exposure in two opposing directions while decreasing it in the opposing directions rotated 90 degrees. You could have this create two bars rotated 90 degrees from each other, or you could create more complex footprint shapes.

But this should give you something to start with that you can make more complex as needed. As a note, this measure also exposes number of stories as an argument while maintaining the total building area. Useful for quick early massing studies where you have program area you want to hit, but may not yet have site selected and are looking at various massing configurations. You can pair this with measures that rotate the building, and fenestration, shading, and constructions.