How do you determine "ride height" to make suspension mods??

So is the only way to really figure out ride height would be as follows:

1) Buy rear tires I plan on using (ouch)
2) Buy rear rims I plan on using ( ouch, but not necessary to buy now if I have the tires?)
3) Set the car on jack stands:
4) While on jack stands establish the full stance rear and front with the rear tires up under the car. (may not nor does not need to be level due to stance)
5) Once stance is established -- Measure floor to fixed point on car and this is my ride height

Why does my creative mind think I can do this with math and my cnc router at work to save the cost of the tires and rims right now: Here me out on this:
I route a disc in MDF -- 18" Diameter to act as the rim
I route a disc in MDF -- 18" center & diameter of tire I plan to use this will act as the tire, hell I can even paint it black so my simple mind doesn't get corn-fused
I then use this wheel / tire MDF mock up to set my ride height.
I can do the both for front and rear (since I have no suspension on the car at all)

Would this basically do the same thing as buying the real parts? Granted I plan to buy the rims and tires (Feb/mar 2011 (tax refund check)) but wasn't planing on doing it now, yet the 4 link is going in now.

Any thoughts on my mock up idea?
Do what I did go to your local tire shop and get a junk tire the size you plan on using and buy 1 wheel. Then from there you know what the finished result would look like. Tire very on size with different rim sizes so your 26" diameter tire will vary from 24" to 28" depending on rim width. I was originally going to run a 315 until I got it on a rim and it wouldn't clear my tubs had to drop down to a 285.