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

Oh and the rear end will end up being the easy part. Just wait until you have a tire on the front end and you can only turn the wheel 1/4 turn before the tires hit the fender. I had a hell of a time getting my tires measured for the front end and I still don't know what I'm going to run exactly. The rear was done in a weekend.