I was going to pour a small concrete patio behind my house. Like 10′ x 12′. I was wondering how thin can I pour it? Would three inches be too thin. I was thinking about framing it up with 2×4′s, and adding some gravel in the area where the patio will be to bring it up, so I can use less concrete. I am going to be doing a big driveway, and a couple walkways, and I was trying to save as much money as I can by pouring...