A 1/4" per foot is standard, therefore in twenty feet the furthest point would be 5" below the high point. You can make it flatter (3 or 4 inch drop) but it would require greater perfection in concrete placement, perhaps beyond reason.
That depends on the roof material. Metal can be as low a 1/12. Fibergglass shingles should be at least 3/12.
225 bricks. 16in * 16in = 256 sq. in. 20ft = 240in. 240in * 240 in = 57,600 sq. in. 57,600 sq. in. / 256 sq. in. = 225. 225 bricks is your answer.
20ft. x 20ft.
20ft
20 ft= 6096 mm (6096 * 6096) / (450 * 450) = 183.512178 184 slabs
For an area that is 20ft by 20ft and you want to add 6 inches of topsoil, you will need 20 cubic yards of topsoil. Topsoil is typically ordered by the cubic yard, so this measurement will ensure that you have enough to cover the entire area with a 6-inch layer.
The answer will depend on the size of the tiles.
20ft
5 yds - One yard of concrete will cover approximately 81 square feet 4" deep.
20ft subtracted by 10in = 10
That depends on how DEEP you want the concrete !
400 square feet