Sorry for slow reply - I've been busy on other things.
I have been doing a bit of homework on what ways are used to dimension slopes, in different contexts and different countries. Far from complete information yet, but initial suggestions for how a Slope Dimension plugin might display the slope.
1. North American Roofing dimensions:
This is where my trigger for suggesting such a Slope Dimension originated, and would probably be the first to implement.
Show as rise per 12" run, but not only in whole numbers.
Fractions can be used in some examples quoted in this topic thread, and by extension, other fractional values - e.g., ¼,⅜, ½,¾
In text show slope as 1/12, 3/12, etc, or ¼/12, in preference to 1:12, 3:12, or ¼:12.
Very steep slopes such as a church steeple can use a denominator much larger than 12 - for example, 60/12.
Use a triangle symbol with a clear background (not white), with or without hypotenuse, e.g.,
flipped horizontally if the slope goes the other way.
Either place text against the sides of the triangle symbol
Options 1a and 1b
or (simpler to program) add on the same level the slope as a ratio, separated by slash, as above.
Option2 (with or without hypotenuse: with is shown)
For visual clarity, the triangle symbol (or its two line replacement) should have its hypotenuse parallel to the slope being dimensioned, the rise vertical, and the run horizontal.
Options for this sort of dimensioning could include, in addition to those currently used in Angular Dimension 2, where relevant, whether to use Option 1 or Option 2 (text separately beside rise and run, or along the slope), and variant triangles type a or b (symbol with or without hypotenuse).
Angular dimension allows for specifying the size or directly picking the radius of a dimension arc.
The equivalent here would be what fraction of 12" to use to scale the dimension symbol and text, with a default of 'full size'.
Two pick points on the slope could alternatively specify the length to use for the base of the dimension triangle, with the third pick point confirming the direction against which to measure the slope - usually, the horizontal x-y plane for a conventional roof slope. Or maybe one should always assume that 'slope' is relative to horizontal? In which case two picks would be enough.
2 European and metric countries roof pitch
I have limited information here. Perhaps a European architect on this forum could amplify the Wikipedia entry I found after searching for 'roof pitch'.
"Countries which use metric measurement systems use a degree angle, or what fall there is per unit of run, and expressed as a '1 in x' slope."
3 Road, rail and civil engineering
In this use case, the angles involved are much smaller, and it seems that the convention is to specify the slope using 1 as the rise (denominator), with the run determining the angle. For example, 1 in 100, 1 in 50.
In this case, the triangle would often be visually indistinguishable from a straight line, and an Option 2 format with the text parallel to the dimensioned slope would be sufficient.
The separator would become the word
in surrounded by spaces.
For this use case, it would be difficult to pick a horizontal direction.
4 General considerations
Perhaps the horizontal base should always be assumed both for engineering and for roofs? So only two picks would be needed, with the horizontal assumed.
Perhaps there could be a user selectable option to choose between the slash and a colon as the separator.
And maybe the program could either offer as options a choice of denominator or numerator as the fixed value (e.g., denominator of 12 for North America, or (say) 5, 10, 20, 50, 100 for metric dimensions; and numerator of 1 for small angles. Perahps also add 'woodworking fraction' denominators, as in SU Fractional or Architectural (Imperial) units - 1/2, 1/4, 1/8, 1/16th etc.
I've also seen a diagram while search for images of roof dimensionsng, with the roof pitch shown in plan view centrally on the roof plane(s). That would be tricky to implement. Perhaps the user could use a predominantly side view to generate the dimension group, then manually rotate it for a plan view?
What about the issue of rounding? If an angle is drawn in SU using the pitch method of input (3:12 for example), instead of an angle in degrees, a SU calculation of the angle will result in a value whose arctangent is an exact integer fraction.
Otherwise the value will be approximate, and (as an angle) preceded by a tilde (~) character. What should the plugin do for approximate values? If either the numerator or the denominator is a fixed value, that isn't a problem - just use a tilde prefix when the result isn't exact.
If however the program tries to 'guess' the nearest fractional representation with a maximum denominator, it gets quickly much more complex - perhaps I shouldn't go there!
All I have time for tonight.
Any comments on these suggestions before I go further on trying to design a Slope Dimension tool?