Hope some of this info helps.
If I have calcutalted right and please correct me if I am wrong. 8 12 inch finished blocks across will be 96 inches wide.
9 blocks down will be 108 inches long.
8x8 will be 96 across and 96 inches long.
The width of your fabric will determine how much fabric you will need for your quilt. You also need to have your backing wider than your top (most say allow 8 inches for length and 8 inches for width. Plus more if you are using the backing to wrap around to the front for your binding.)(4 inches for top & 4 for bottom and 4 inches extra on each side)
There are fabrics that come in wide widths. Some are at least 108 inches wide. In cases like that you just need the length of your quilt top plus your 8 extra inches if you are using a seperate binding piece.
Here are some links that might help explain it better
www.ehow.com/way_5805308_much-backing-needed-queen-quilt_.html or
www.quilt-lovers-guide.com/quilt-backing.html