5
4x8=32
Technically Yes, but you'll need to check with your building inspector because there are codes regarding structure that vary from place to place, and the inspector isn't going to pass something based on my say so.The old rule of thumb was 1 inch for 1 foot, so a 12 foot span would require a 2 x 12.A 4 x 8 isn't equal to a 2 X 16, or even 2 2 X 8's, but it should do if the load isn't too great.I'm guessing you want to go with 8" stock because you've got some headroom issues. You'd be better off structurally with an LVL (Laminated Veneer Lumber) or OSB (Oriented strand Beam) or a truss, but these are kind of pricey.If you get in trouble see if they'll let you go with them on 12" centers.
32
41
A 30 foot circle covers about 707 square feet. 23 pieces would technically cover that. I'd get 30 of them so I wouldn't have to cut any of them.
Should be able to squeeze it into a 4x8, 4x10. Draw it out using a scale of 1/4" = 1 foot before you start.
8
$4.44 for a sheet of 4x8 1/2 in drywall at menards in Morris Illinois
Its maths
That depends - whether your 4x8 bricks are in centimetres, metres, inches or feet.
1 square foot 12X12 = 144 square inches Brick 4x8= 32 square inches 200x144 divided by 32 = 900 Brick