Equilateral triangle:
> Side length is $3/3=1$m, area of equilateral triangle is given by $\dfrac{s^2\sqrt3}4$ so area is $\boxed{\dfrac{\sqrt3}4\approx0.433}$
Square:
> Side length is $3/4=\frac 34$m, area of square is given by $s^2$ so area is $\boxed{\dfrac 9{16}\approx0.563}$
Circle:
> Circumference of $3$ gives radius of $\dfrac3{2\pi}$, area of circle is given by $\pi r^2$, so area is $\boxed{\dfrac9{4\pi}\approx0.716}$
Storage containment structures are round due to the fact that round structures have the ability to withstand more stress. Also, as you can see from the results, they can maximize the area of a structure using the least amount of material.