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.
If the slope is in the 8' direction (which would be the usual) the pitch would be 1/8 to 1/4 " per foot (preferably 1/4" per foot) so 8 x 1/4" = 2"lower at the outer edge than where it touches the house. always best to pitch 1/4 " at least.
Also -
Larger sections of concrete can have less slope. The finisher has to know what he is doing. I've done 100s of yards using 1" in 10' as a minimum.
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
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
To answer this, I have to assume that your container is a perfect cube. 20ft is 6.096m. this to the power of 3 is 226.535m3