The answer will depend on the units used for the measurement of the room as well as the size of the plywood sheets. And since you have not bothered to share those crucial bits of information, I cannot provide a more useful answer.
7x1=7, 7x2=14, 7x3=21, 7x4=28,7x5=35, 7x6=42, 7x7=49, 7x8=56,7x9=63, 7x10=70, 7x11=77, 7x12=84,7x13=91, 7x14=91, 7x15=105, 7x16=112,7x17=119, 7x18=126, 7x19=133, 7x20=140,7x21=147, 7x22=154, 7x23=161, 7x24=168,7x25=175, 7x26=182, 7x27=189, 7x28=196,7x29=203, 7x30=210, 7x31=217, 7x32=224,7x33=231, 7x34=238, 7x35=245, 7x36=252,7x37=259, 7x38=266, 7x39=273, 7x40=280,7x41=287, 7x42=294, 7x43=301, 7x44=308,7x45=315, 7x46=322, 7x47=329, 7x48=336,7x49=343, 7x50=350, 7x51=357, 7x52=364,7x53=371, 7x54=378, 7x55=385, 7x56=392,7x57=399, 7x58=406, 7x59=413, 7x60=420,7x61=427, 7x62=434, 7x63=441, 7x64=448,7x65=455, 7x66=462, 7x67=469, 7x68=476,7x69=483, 7x70=490, 7x71=497