That works unless you have a rolled cylinder, or it doesn't work for me
With a rolled cyclinder, if you have a rolled and flat configuration, and
have your part set to rolled, change the diameter of the cylinder, and then
rebuild, the length property will not change until you activate that
configuration. Unless I'm missing something else...
What I do is just create a construction line in a sketch and give it a
dimension that is tied to an Equation that calculates the length or width.
If it is a cylinder, it calcs the length of the arc, based on the bend
factor. Rude and crude, but it has worked for 3 years this way.