I have a very large garage and plan to enclose the back portion. The area will be roughly 400sq ft (16 x 25). The problem is there is a 3 inch slope from the back to the front of the area. The surface is smooth concrete with no cracks. I live in FL so there is no freezing.

What is the best way to level the floor when taking into account the large area?
What is the most economical way? I don't want to put down a wood sub floor.

I've seen floor leveling compounds but not sure if they can cover a 3 inch depth.
Is it a bad idea to correct a big portion of the leveling with poured concrete and then finish with a leveling compound of about 1/2 inch?

Thanks for your help!

Your best bet would be to level the entire area with another cement pour. The leveling material will not give you the needed slope fill. Question, do you need to level the floor?

Think this may be what you're looking for -- self leveling

Floor Underlayments by Hacker Industries Inc. - underlayment - 800.642.3455 (http://www.hackerindustries.com/)

Maybe someone else has a better idea -- Watch the video Floor

Floor Underlayments - Hacker Industries Inc. - 800.642.3455 - Video (http://www.hackerindustries.com/video.htm#)