Incremental Values

When building Revit families, it´s quite useful to be somewhat in control of the user inputs... for instance, doors come at certain width´s, it could be 810, 910 ,1010 mm´s or 3-0"´, 3-6", 4´-0" etc.

You´ll need a few parameters:

User Dim (Length) - What the end user is gonna use
Increment (Length) - 100 mm/6" - Not neccecary, it could be a fixed value in the comming parameters
Integer (Integer) Formula = User Dim / Increment
True Dim (Length) Formula = Integer * Increment

Now, just dimension your geometry/ref. planes with the True Dim parameter

Note 1: If needing the scandinavian standards of 810, 910 mm etc. ? just add + 10 to the True Dim parameter: = (Integer * Increment) + 10
Note 2: If you want to control how User Dim gets rounded up, or down just add either +0.49 or -0.49 to the True Dim parameter: (Integer * Increment) + 0.49 or (Integer * Increment) - 0.49