Height. Think about how you plan to use your finished basement. If you want to exercise down there, you may need more headroom. Lift your arms overhead. I need an 8-foot ceiling to do that. Will you be standing on a treadmill? Add the height off the floor to your height. If you're actually going to run on the treadmill instead of posing for fake exercise Facebook photos, you'll need even more room since you'll bounce up as you run. Often the height just isn't there.