Actually only a handful of people have done this surprisingly.
Geometry of a square ratio cutting area is actually more favorable because it avoids the extreme edges of the sheet, which are harder to get accurate.
You can just use the regular frame with 10’ top cross bar and 4x4 cut area or if you really need the space you can probabaly use something as small as a 6’ top motor mount
8’ top motor mount would be a good compromise IMHO.
above post is probably most detailed plans for 4x4.