$\left ( {1} \right )$

$8\div 2=4\left ( {cm} \right )$

$3.14\times {4}^{2}+3.14\times 8\times 20$

$=3.14\times 16+3.14\times 8\times 20$

$=50.24+502.4$

$=552.64\left ( {{cm}^{2}} \right )$

$\left ( {2} \right )$

$3.14\times {4}^{2}\times 20$

$=50.24\times 20$

$=1004.8\left ( {立方厘米} \right )$

$=1004.8\left ( {毫升} \right )$

答：$\left ( {1} \right )$做布套至少用了$552.24{cm}^{2}$布料；$\left ( {2} \right )$这个水杯约能装$1004.8$毫升水.