I could live with your first two suggestions.
I have included a picture of our standard 2D detail.
Can you have fractions? You suggest ¼:12. Wouldn't that be better as 1:48? Or is that not the convention?
We commonly use; ¼:12, 3/8:12, ½:12 & 5/8:12. US convention does not use 1:48. On very rare occasions one will see oddball non-integer fractions, but I don’t have an example, handy.
How would you want to show a slope for an angle that hasn't got integer rise and run? You probably know (as I half remembered, and then checked) that you can input an angle AS a slope - 1:6, 5:12 for example - to the Protractor or Rotate tools when you create a roof slope, and that could be shown as an exact ratio, either to base :12, or simplified from (for example 6:12) to 1:2. If only approximately an integer value, the slope dimension could be preceded by a tilde (~) character, as SU does for approximate values.
I use the ratio method of setting angles often for roof pitches. It is very handy, once it was pointed out to me.
James “Jim” Hannah