Mic-pa is correct. a twelve foot table can handle width of 120 inches and length is immaterial. bear in min that a quilt of your size cannot be turned for borders. talk to a Lon armed.

A 12 ft table is 144" wide of which approx. 136" is usable. I have never had a quilt that filled my 12 ft table. Since most Professional LAQ's have 12'tables you should not have a problem.
Also, of you round the corners using a plate, after its quilted, this will solve the problem of corners that stick out.

My table is only 10 feet. I can't take anything larger than 100 inches across. I've quilted 120 inches long, but my max across is still 100. Check with your LA to see what their max is. If you still want to make it wider than they can handle, try to find another LA who can accomodate you.

Excellent suggestion!

Just my two cents worth -- a 12 foot table doesn't really mean that you have a full 144 inches of quilting space. The machine itself eats up about 6 to eight inches of width and you have to allow that for both sides of the table, since the machine slides from one end to the other. You also have to allow for 3 to 4 inches on either side for clamping (if you use clamps). So about eighteen to twenty inches of table space has to be allocated to "administrative" space that can't be used as quilting space. So the absolute most quilting space that can be efficiently used is about 120 to 124 inches across the width, if the quilt is perfectly square, which is not common. Not because of poor piecing, but because that is just the nature of quilting. I hope this explains a little about why a 12 foot table cannot accomodate a 12 foot quilt top.

You can all hit me with a bat, but I have to say this -- I genuinely sympathize with the quilter who did not get her quilt fully quilted and was charged more (I truly cringe when I think of how unfairly and how poorly she was treated and I am embarrassed for the longarmer who did this) for the longarmmer's shoddy work. It should have never happened.

Except the corners at the foot end, which will hang down farther unless you round them off. Think of it as a diagonal line from the corner of the mattress to the corner of the quilt. The length across the diagonal of a 4-sided figure is greater than the sides.