My sister has made a couple of covers for regular machines. I'll tell you what she does to see if that helps. She measures the length, height, and width of the machine (for a LA that would include the handles, laser, connections, thread holders, etc.) Add a couple of inches to the measurements to be sure it will fit easily over the machine. She constructs them like you would a tote bag without the handles, if that makes sense. And she does box the ends of the closed side. It fits ovet the machine like an upside down tote bag.
I'm thinking that it would look really good if orphaned quilt blocks were incorporated into the cover, so I might try that.