This is a Revit 2010 parametric helix family for you to download and abuse. It's good for about 3 full rotations (1080 degrees) before you start having and visible artifacts. You can think of this in some ways as another basic sketch tool like the ones you have in the draw gallery. Just as you would draw an arc, put a profile on it, and make a sweep, you can use this to draw a helix, host profiles on it, and make forms. This includes being able to make in-place sweeps in the .rvt environment of whatever category you want.
To operate, load the mass family into a project and you get a single model line curve. Select the curve and manipulate the 4 parameters to determine the angle of rotation, start and end radius, and height of your helix, either with the shape handles or numerically. You can then use the line for making sweeps and blends or whatever else you fancy. Or you can create geometry IN the family and place complete and flexible forms in the host file.
I won't do a tutorial for how to make this one, but just show the basic principles. If you're curious, you can dissect the family and expand on it if you want more rotations or other functionality. The basic principles are ones that Matt Jezyk and Phil Read started using years ago to make rotated floor plates for tall buildings and has been adapted by others for many other purposes. This family reduces the methodology to a basic geometric primitive that you can use for whatever purpose you like: buildings, ramps, shock absorbers, whatever.
The basic building block of this family is a line that has a vertical offset parameter and a horizontal rotation. I've placed a point on the end of the line and set it to be visible just to make the start and end easier to identify.
The height and rotation of the line is driven by an integer value, so the higher the number, the higher the line and the farther it is rotated. Additionally, the length of the line varies according to the same integer. This allows the length to expand and contract depending on where it is in the helix.
This line is then loaded into a second mass and 17 instances are placed in the same spot. After assigning an integer value 0 through 16, each instance rotates and raises to it's unique placement in the family
The endpoints are sewn together using a spline by points model line. The loaded line family then has it's visibility parameter set to off, so only the spline will show when it is loaded into a project. You can increase the "resolution" of this family, how closely it creates a perfect circle, by adding more lines and increasing the integer value of each, but with 16 increments it's pretty damn round through 3 rotations.