I would recommend checking out quikrete calculator on their website to confirm but for the size you are mentioning I would suggest 34 - 35 bags for 3" thick on 80sf.
The aggregate may be too large for the small projects
Each 80 lb bag of QUIKRETE® Concrete Mix will yield approximately 0.6 cu ft. For a 6’ diameter circle 6” thick, you will need 4.32 cubic feet of concrete for each inch of width, or 7.2 80-pound bags. If your wall is 6”x 6”, therefore, you will need 44 80-pound bags. Yields are approximate and will vary with waste, uneven subgrade, etc.
Depending on where you are geographically, the QUIKRETE® Concrete Mix may not contain gravel. In certain markets, the concrete is preferred without gravel for workability. In these areas, the mix design is compensated to achieve the specified strength.
Each 80 lb bag of QUIKRETE® Concrete Mix will yield approximately 0.6 cu ft. For a 3’ by 3’ slab at 4” thick, you will need 3 cubic feet of concrete 5 80-pound bags of concrete. Yields are approximate and will vary with waste, uneven subgrade, etc.
You need concrete footing, metal bars/rebar, leveling tools, and trowel. If you're asking about material quantity, take your drawings or dimensions with roof design including roof pitch to a local lumberyard or box store and request a take-off. A take-off will give you a complete list of what you'll need to build your structure.
50 bags of 80 lb concrete mix you need 12.00 * 10.00 * 0.25 = 30.00 cubic feet of concrete an 80 lb bag of concrete mix is .6 cubic feet you need 30.00 / .6 = 50.00 bags of 80 lb concrete mix
134 if it is 4" thick