Bricks, Masonry, Asphalt and Concrete - Concrete Slab on a Hill

I am considering pouring a 9 ft square free standing concrete slab to support a Hot Tub. The ground is not level it goes up about 18 inches over the 9 foot run. I dug the hole about 22 inches deep on the high end of the slope and 4 inches on the low end. I planned on using plywood for the forms about 20 inches on each side and using 4 inches of stone on the bottom. I want to go up the 20 inces so the tub will be level with the deck.

Most of the information I read talks about 4 or 6 inch slabs. Is there anything different I need to know if I am planning on a 20 inch slab. Do I need more levels of wire mesh. I am a novice at this so any suggestions will be helpful

Thanks

not much need for a 20 in slab, just form in a beam on the edges and low end to raise the base of the slab to level for your hill, use concrete sand to fill the center and level it out in lifts of 3-4 inches. pack each lift firmly with a tamper and then use only one layer of wire in your pad. you can use 20 in of concrete but that is a lot of unnessary expence if you do wire should be about 3 in from the top of the pad.

if we're not supposed to eat animals why are they made out of meat?

Thanks for the insight, but I am new to this and still learning. When you say form in a beam. Do you mean - on the low end and the sides create a cement barrier maybe 8 inches wide and 16 inches high then fill the center. Or even keep it low and build up with cider block.

Then but the cement slab on top