I'm thinking of putting a flagstone patio in my yard under a Magnolia tree. The grass won't grow well at all and when the leaves or flowers fall they cover everything I would like to cover a 30 by 30 foot square how much will I need to buy 900 square ft. Thinking 1 to 1.5 in. Thick. Live in Northwest

Add up to 20 percent for waste, 1080 sq ft.

How many square feet do you think you can get out of 1 ton? Would sand be ok for the foundation?

You might get 100 sq ft of 1 1/2" might be a good question for the supplier. In the northwest you have to be concerned with water and freezing. To do it right, you remove all the top soil and replace it with gravel for drainage and some place for the water to go and compact that and then set the stone over about 1" of sand.

Thanks for the advice. Now I just need to find a supplier that sells flagstone at a cheap price around Tacoma wa. Anyone know a good supplier that's cheap.

The terms "good supplier" and "cheap" are rarely found in the same sentence. Meaning you usually get what you pay for.

Also, I think nealtw's numbers might be a bit misleading. For 100 S.F. at 1-1/2" thick (0.125'), the volume computes to 12.5 C.F. Normal flagstone, having a density of 95 Lb. per C.F., will weigh about 1188 Lb., rounded. Quite a bit shy of the 1 ton yield you asked about.

Conversely, 1 ton at the above density should result in material about 0.21' thick, or about 2-1/2".

The trouble with doing the math here is the stone in the pallet that you buy. If you buy 1" stone , is that the avareage thickness or the min. thickness? That's why I said talk to the supplier about his product.
http://www.schwartzstone.com/flagstn.html